Method and equipment for handover

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A method and equipment for handover are provided. The method includes informing, by a source base station, a source core network whether a direct data forwarding path is available, determining, by the source core network, whether to use direct data forwarding or indirect data forwarding, informing, by the source core network, a target core network of information of direct data forwarding, indirect data forwarding or data forwarding being not possible, informing, by the target core network, a target base station of the information of direct data forwarding, indirect data forwarding or data forwarding being not possible, and allocating, by the target base station, tunnel information for data forwarding.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. §119(a) of a Chinese patent application number 201811467666.2, filed onDec. 3, 2018, in the Chinese National Intellectual PropertyAdministration, and of a Chinese patent application number201910094153.X, filed on Jan. 30, 2019, in the Chinese NationalIntellectual Property Administration, and of a Chinese patentapplication number 201910245257.6, filed on Mar. 28, 2019, in theChinese National Intellectual Property Administration, the disclosure ofeach of which is incorporated by reference herein in its entirety.

BACKGROUND 1. Field

The disclosure relates to wireless communication technologies. Moreparticularly, the disclosure relates to a method and equipment forhandover.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

Modern mobile communications increasingly tend to focus on multimediaservices that provide users with high-rate transmission. FIG. 1 is asystem architecture diagram showing System Architecture Evolution (SAE)according to the related art.

Referring to FIG. 2, a User Equipment (UE) 101 is a terminal equipmentfor receiving data. An Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) 102 is a radio access network in which a macroeNodeB/NodeB providing the UE with an interface for accessing the radionetwork is included. A Mobility Management Entity (MME) 103 isresponsible for managing a mobility context, a session context andsecurity information for the UE. A Serving Gateway (SGW) 104 mainlyfunctions to provide a user plane, and the MME 103 and the SGW 104 maybe in a same physical entity. A Packet Data Network Gateway (PGW) 105 isresponsible for charging, lawful interception or more, and the PGW 105and the SGW 104 may also be in a same physical entity. A Policy andCharging Rules Function Entity (PCRF) 106 provides Quality of Service(QoS) policy and charging rules. A Serving GPRS Support Node (SGSN) 108is a network node device providing routing for data transmission in aUniversal Mobile Telecommunication System (UMTS). A Home SubscriberServer (HSS) 109 is a home ownership subsystem of the UE, and isresponsible for protecting user information comprising the currentlocation of the UE, the address of a serving node, user securityinformation, a packet data context of the UE, or more.

FIG. 2 shows an overall architecture of 5th generation (5G).

Referring to FIG. 2, a User Equipment (UE) 201 is a terminal equipmentfor receiving data according to the related art.

A Next Generation Radio Access Network (NG-RAN) 202 is a radio accessnetwork in which a base station providing the UE with an interface foraccessing the radio network is included. The base station may be a gNBor an eNB connected to 5G core (5GC), and the eNB connected to 5GC mayalso be called an ng-eNB. An Access Control and Mobility ManagementFunction Entity (AMF) 203 is responsible for managing a mobility contextand security information for the UE. A User Plane Function Entity (UPF)204 mainly provides a user plane function. A Session Management FunctionEntity (SMF) 205 is responsible for session management. A Data Network(DN) 206 contains operator services, the access to Internet, third-partyservices or more.

The interface between the NG-RAN and the AMF is NG-C or N2, and theinterface between the NG-RAN and the UPF is NG-U or N3.

In the next generation network deployment, there is a scenario in whichthe LTE network and the 5G network coexist. When a UE moves in aboundary between the E-UTRAN and the NG-RAN, technologies for realizinga handover between different radio access technologies (inter-RadioAccess Technology (RAT) handover) are required in order to ensure thecontinuity of services. There are two different schemes for dataforwarding during the handover between two systems, since there is aconcept of Evolved Packet System (EPS) bearers in an EPS system but noconcept of EPS bearers in a 5G System (5GS).

One scheme is a method of using one data forwarding tunnel for eachProtocol Data Unit (PDU) session between the NG-RAN node and the UPF.For the handover from 5G to 4G, the UPF sends the data flow of differentQoS flows received from each PDU session tunnel to the correspondingEvolved Radio Access Bearer (E-RAB) tunnel and sends it to the SGW, andthe SGW forwards it to the eNB. For the handover from 4G to 5G, the UPFsends the data received from each E-RAB tunnel to the corresponding PDUsession tunnel, and the data is sent by the UPF to the NG-RAN node.

The other scheme is to establish a data tunnel of each E-RAB between theNG-RAN node and the UPF, so that the data forwarding between the NG-RANnode and the eNB is performed through each E-RAB tunnel between theNG-RAN and the UPF, between the UPF and the SGW, and between the SGW andthe eNB. This data forwarding method may also forwards data directlybetween the NG-RAN node and the eNB without using the core network.

If these two data forwarding methods are adopted at the same time, howto ensure the coexistence and interoperability of the two dataforwarding methods in the network has not been discussed yet.

In the handover process of the EPS and the 5GS, the allocation of dataforwarding tunnels and the execution of data forwarding involve toNG-RAN node, SMF, UPF, SGW, and eNB. If there are two different dataforwarding methods at the same time, the interoperability betweendifferent nodes is a problem to be solved, and if one equipment andanother equipment support different data forwarding methods, this willresult in the failure of data forwarding, especially when the aboveequipment is from different vendors.

The above information is presented as background information only toassist with an understanding of the disclosure. No determination hasbeen made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the disclosure.

SUMMARY

Aspects of the disclosure are to address at least the above-mentionedproblems and/or disadvantages and to provide at least the advantagesdescribed below. Accordingly, an aspect of the disclosure is to providea method and equipment for supporting handover in view of thedeficiencies of conventional approaches.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

In accordance with an aspect of the disclosure, a method for supportinghandover is provided. The method includes the operations of informing,by a source base station, a source core network whether a direct dataforwarding path is available, determining, by the source core network,whether to use direct data forwarding or indirect data forwarding,informing, by the source core network, a target core network ofinformation of direct data forwarding, indirect data forwarding or dataforwarding being not possible, informing, by the target core network, atarget base station of the information of direct data forwarding,indirect data forwarding or data forwarding being not possible, andallocating, by the target base station, tunnel information for dataforwarding.

Specifically, the target base station allocates a corresponding dataforwarding tunnel according to whether it is direct data forwarding orindirect data forwarding. if it is direct data forwarding, the targetbase station allocates downlink data forwarding tunnel information forthe mapped E-RAB, for the QoS flows for which the target base stationaccepts data forwarding or the E-RAB for which the target base stationaccepts data forwarding, if it is indirect data forwarding, the targetbase station allocates downlink data forwarding tunnel information forthe PDU session to which the QoS flow belongs, for a QoS flow for whichthe target base station accepts data forwarding.

Specifically, the method further includes the operation of sending, bythe target bases station, the allocated data forwarding tunnelinformation to the target core network.

In accordance with another aspect of the disclosure a method forsupporting handover is provided The method includes the followingoperations of sending, by a source base station, a source base stationidentifier to a source core network, sending, by the source corenetwork, the source base station identifier to a target core network,sending, by the target core network, the source base station identifierto a target base station, and determining, by the target base station,whether direct data forwarding is available, and allocating, by thetarget base station, a corresponding data forwarding tunnel.

Specifically, the method further includes the operation of sending, bythe target base station, information of direct data forwarding beingavailable to the target core network.

Specifically, the method further includes the operation of sending, bythe target core network, information of direct data forwarding beingavailable to the source core network.

In accordance with another aspect of disclosure, a method for supportinghandover is provided. The method includes the following operations ofsending, by a source base station, a data forwarding manner support bythe source base station to a source core network, and allocating, by thesource core network, data forwarding tunnel information according thedata forwarding manner support by the source base station.

Specifically, the data forwarding manner comprises data forwarding of aPDU session tunnel and/or data forwarding of an E-RAB tunnel.

In accordance with another aspect of the disclosure, a method forsupporting handover is provided. The method includes the followingoperations of sending, by a UPF, a data forwarding manner support by theUPF to an SMF, sending, by the SMF, the data forwarding manner supportby the UPF to an AMF, sending, by the AMF, the data forwarding mannersupport by the UPF to a target NG-RAN node, and allocating, by theNG-RAN node, data forwarding tunnel information according the dataforwarding manner support by the UPF.

Specifically, the data forwarding manner comprises data forwarding of aPDU session tunnel and/or data forwarding of an E-RAB tunnel.

The methods for supporting handover in the present application, maysolve the above problems, such that the problem of coexistence ofdifferent data forwarding methods when the UE moves between the EPS andthe 5GS system is completely solved, thereby avoiding data loss,ensuring service continuity and interoperability of different equipmentfrom different vendors, and reducing configuration by an operator.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the disclosure will be more apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a system architecture diagram showing a System ArchitectureEvolution (SAE) according to the related art;

FIG. 2 shows a schematic diagram of an initial overall architecture of5G according to the related art;

FIG. 3 shows a schematic diagram of a first method for supportinghandover according to an embodiment of the disclosure;

FIG. 4 shows a schematic diagram of a first embodiment of a first methodfor supporting handover according to an embodiment of the disclosure;

FIG. 5 shows a schematic diagram of a second embodiment of a firstmethod for supporting handover according to an embodiment of thedisclosure;

FIG. 6 shows a schematic diagram of a second method for supportinghandover according to an embodiment of the disclosure;

FIG. 7 shows a schematic diagram of a third method for supportinghandover according to an embodiment of the disclosure;

FIG. 8 is a schematic diagram of a fourth method for supporting handoveraccording to an embodiment of the disclosure;

FIG. 9 is a schematic diagram of a fifth method for supporting handoveraccording to an embodiment of the disclosure; and

FIG. 10 is a schematic diagram of a sixth method for supporting handoveraccording to an embodiment of the disclosure;

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thedisclosure. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of thedisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of thedisclosure is provided for illustration purpose only and not for thepurpose of limiting the disclosure as defined by the appended claims andtheir equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

It should be understood by one person of ordinary skill in the art thatsingular forms “a”, “an”, “the”, and “said” may be intended to includeplural forms as well, unless otherwise stated. It should be furtherunderstood that terms “include/including” used in this specificationspecify the presence of the stated features, integers, operations,elements and/or components, but not exclusive of the presence oraddition of one or more other features, integers, operations, elements,components, and/or combinations thereof. It should be understood that,when an element is referred to as being “connected to” or “coupled to”another element, it may be directly connected or coupled to otherelements or provided with intervening elements therebetween. Inaddition, “connected to” or “coupled to” as used herein may includewireless connection or coupling. As used herein, the term “and/or”includes all or any of one or more associated listed items orcombinations thereof.

Those skilled in the art will appreciate that all terms (includingtechnical terms and scientific terms) used herein have the same meaningas commonly understood by one of ordinary skill in the art belonging tothe field of the art, unless otherwise defined. It should also beunderstood that those terms, such as those defined in a generaldictionary, should be understood as having a meaning consistent with themeaning in the context of the prior art, and it is not intended to beconstrued in an idealized or overly formal sense unless specificallydefined herein.

Those skilled in the art may understand that the “terminal” and“terminal equipment” as used herein include both a wireless signalreceiver device only having a wireless signal receiver without atransmitting capability, and a receiving and transmitting hardwarehaving a device capable of receiving and transmitting hardware fortwo-way communication over a two-way communication link. Such device mayinclude: a cellular or other communication device having a single linedisplay or a multi-line display, or a cellular or other communicationdevice without a multi-line display; a PCS (Personal CommunicationsService), which may combine voice, data processing, fax and/or datacommunication capabilities; a PDA (Personal Digital Assistant), whichmay include a radio frequency receiver, a pager, Internet/Intranetaccess, a web browser, a notepad, a calendar, and/or a GPS (GlobalPositioning System) receiver; a laptop and/or a palmtop computer orother devices having and/or including a radio frequency receiver. Asused herein, “terminal” and “terminal equipment” may be portable,transportable, installed in a vehicle (in aviation, sea and/or land), oradapted and/or configured to operate locally, and/or operated in anyother position on the earth and/or space in a distributed form. As usedherein, “terminal” and “terminal equipment” may also be a communicationterminal, an internet terminal, and a music/video playing terminal, forexample, a PDA, a MID (Mobile Internet Device), and/or a mobile phonehaving a music/video playback function, and may also be a smart TV, aset-top box and other devices.

In the process of UE handover between EPS and 5GS, there are threemanners to coexist two data forwarding methods:

Manner 1: the first method is used for indirect data forwarding, thatis, a method of using one data forwarding tunnel for each PDU sessionbetween the NG-RAN node and the UPF is used; and the second method isused for direct data forwarding, that is, direct data forwarding isperformed between the NG-RAN node and the eNB through a E-RAB tunnel.

Manner 2: when to use which data forwarding method is not limited in thestandard, and which data forwarding method is supported depends on theimplementation of an equipment vendor.

Manner 3: both data forwarding methods must be supported.

Direct data forwarding may be performed only when the eNB and the NG-RANnode have a direct path or a secure connection. Corresponding to theforegoing manner 1, in the process of handover from EPS to 5GS, if it isdirect data forwarding, the target NG-RAN node needs to allocate dataforwarding tunnel information for the E-RAB corresponding to the QoSflow for which the target base station accepts data forwarding, and theinformation is included in the handover request acknowledgement message;if it is indirect data forwarding, the target NG-RAN node needs toallocate data forwarding tunnel information for the PDU session to whichthe QoS flow for which the target base station accepts data forwardingbelongs, and the information is included in the handover requestacknowledgement message. However, in conventional approaches, the NG-RANnode does not know whether there is a direct path or a secure connectionbetween the eNB and the NG-RAN node.

In the process of handover from EPS to 5GS, if it is direct dataforwarding, the AMF sends the tunnel for each E-RAB allocated by thetarget NG-RAN node to the MME, and sends it to the source eNB throughthe MME; if it is indirect data forwarding, the AMF needs to send thedata forwarding tunnel information for each PDU session allocated by thetarget NG-RAN node to the UPF through the SMF, and the SMF or the UPFallocates a data forwarding tunnel for each E-RAB used for dataforwarding from SGW to UPF. It may be seen that for the two dataforwarding methods, the behaviors of the UPF are different, but the UPFdoes not know whether the eNB and the NG-RAN node have a direct path ora secure connection, so the UPF does not know whether to allocate a dataforwarding tunnel.

The first method for supporting handover according to the presentapplication is shown in FIG. 3.

FIG. 3 shows a schematic diagram of a first method for supportinghandover according to an embodiment of the disclosure.

Referring to FIG. 3, the method solves the above two problems, such thatdata forwarding in the handover process between different systems issuccessfully performed. Detailed descriptions of operations unrelated tothe present embodiment are omitted herein. The method includes theoperations of:

Operation 301: the source base station informs the source core networkof whether a direct data forwarding path is available. The source basestation may determine whether direct data forwarding path is availablebased on whether there is a direct interface or a security connectionbetween the source base station and the target base station. The sourcebase station may also determine whether direct data forwarding isavailable in consideration of other factors, without affecting the mainconcept of the application. The source base station informs the sourcecore network of whether direct data forwarding path is available by ahandover required message.

The source base station proposes downlink data forwarding. The downlinkdata forwarding proposed by the source base station is per Evolved RadioAccess Bearer (E-RAB).

Operation 302: the source core network determines direct data forwardingor indirect data forwarding. The core network determines direct dataforwarding or indirect data forwarding based on information on whetherdirect data forwarding path is available, which is received from thesource base station. If direct data forwarding is unavailable, thesource core network determines whether indirect data forwarding isfeasible. If both direct data forwarding and indirect data forwardingare not feasible, data forwarding is not possible.

Operation 303: the source core network informs the target core networkof information of direct data forwarding or indirect data forwarding.The source core network may also inform the target core network ofinformation that data forwarding is not possible.

Operation 304: the target core network informs the target base stationof information of direct data forwarding, indirect data forwarding, ordata forwarding being not possible. The target core network informs,through a handover request message, the target base station of directdata forwarding or indirect data forwarding or data forwarding being notpossible.

Operation 305: the target base station allocates tunnel information fordata forwarding. If the target base station accepts the downlink dataforwarding proposed by the source base station, the target base stationallocates tunnel information for downlink data forwarding. The targetbase station allocates a corresponding data forwarding tunnel accordingto whether it is direct data forwarding or indirect data forwarding. Ifit is direct data forwarding, target base station allocates downlinkdata forwarding tunnel information for the mapped E-RAB, for the QoSflows for which the target base station accepts data forwarding or theE-RAB for which the target base station accepts data forwarding. If itis indirect data forwarding, the target base station allocates downlinkdata forwarding tunnel information to the PDU session to which the QoSflow belongs, for a QoS flow for which the target base station acceptsdata forwarding. If data forwarding is not feasible, the target basestation does not need to allocate data forwarding tunnel information.

The target base station knows whether it is direct data forwarding orindirect data forwarding based on the handover request message receivedfrom the target core network.

Operation 306: the target bases station sends the allocated dataforwarding tunnel information to the target core network. For differentdata forwarding methods in operation 305, the data forwarding tunnelinformation may be for each PDU session or for each E-RAB. The dataforwarding tunnel information includes downlink data forwarding tunnelinformation and/or uplink data forwarding tunnel information.

Operation 307: for direct data forwarding, the target core network sendsthe data forwarding tunnel information allocated by the target basestation to the source core network. For indirect data forwarding, thetarget core network allocates the data forwarding tunnel informationused between the source core network and the target core network andsends it to the source core network.

Operation 308: for direct data forwarding, the source core network sendsthe data forwarding tunnel information received from the target corenetwork to the source base station. For indirect data forwarding, thesource core network allocates data forwarding tunnel information usedbetween the source base station and the source core network and sends itto the source base station.

The source base station forwards the data according to the received dataforwarding tunnel information. The target base station receives theforwarded data. The target base station first sends the forwarded datato the UE, and then sends new data received from the target corenetwork.

As such, the description of the first handover method of the applicationis completed, and the problem of coexistence of different dataforwarding methods when the UE moves between the EPS and the 5GS systemis completely solved by the method, thereby avoiding data loss, ensuringservice continuity and interoperability of different equipment fromdifferent vendors, and reducing configuration by an operator.

The first embodiment of the first method for supporting handover in theapplication is shown in FIG. 4.

FIG. 4 shows a schematic diagram of a first embodiment of a first methodfor supporting handover according to an embodiment of the disclosure.

Referring to FIG. 4, in the method, the SMF or the AMF sends theinformation of whether it is direct data forwarding or indirect dataforwarding to the target base station, so that the target base stationdetermines how to allocate the data forwarding tunnel information. Themethod solves the above two problems, so that data forwarding in thehandover process is successfully performed, and different entities inthe network work in coordination to ensure successful data forwarding.Detailed descriptions of operations unrelated to the embodiment areomitted herein. This embodiment is for the handover from EPS to 5GS,including the operations:

Operation 400: the E-UTRAN determines to hand over a UE to an NG-RAN.

Here, the E-UTRAN may be an eNB connected to the EPC. The NG-RAN may bea gNB, or a central unit (CU) in the eNB or gNB connected to the 5GC.The eNB connected to the 5GC may also be referred to as an ng-eNB.

The user plane path before handover is PGW-U+UPF (the UPF having thefunction of the PGW user plane, hereinafter referred to as UPF), the SGWto the E-UTRAN. The SGW needs to support the interface to connect withPGW-U+UPF. The UE has one or more PDU sessions in progress. Each PDUsession includes one or more EPS bearers. In a PDU session establishmentprocess or an EPS bearer establishment process, the mapped QoSinformation and/or the QoS flow identifier of the QoS flow are allocatedfor the EPS bearer. The default EPS bearer is mapped to a non-guaranteedbusiness rate (non-GBR) QoS flow. The QoS information and/or the QoSflow identifier of the QoS flow mapped to the EPS bearer may beallocated by the function of the PCC or the PGW control plane. In orderto support handover between different systems, the function of the PGWcontrol plane may further have an SMF function. In the scene ofdeploying the PCC, the policy control and charging rules function (PCRF)provides the QoS information and/or QoS flow identifier of the QoS flowmapped to the EPS bearer to the SMF. In order to support handoverbetween different systems, the PCRF may also have a policy controlfunction (PCF). The SMF sends the QoS information and/or QoS identifierof the QoS flow mapped to the EPS bearer to the UE through the MME, forexample, sending them to the UE through a non-access layer message PDNconnection establishment message. During the PDU session establishmentprocess or the EPS bearer establishment process, the SMF may also sendthe QoS information and/or QoS flow identifier of the QoS flow mapped tothe EPS bearer to the E-UTRAN through the MME. The E-UTRAN may send themapping information to the UE through an RRC message. The E-RAB and EPSbearer identifiers are the same or one-to-one correspondence, which arereferred to as an EPS bearer in the core network, and are referred to asan E-RAB in the access network. The E-RAB identifier and the EPS beareridentifier are the same or one-to-one correspondence, which are referredto as an EPS bearer identifier in the core network, and are referred toas an E-RAB identifier in the access network.

Operation 401: the E-UTRAN sends a handover required message to the MME.The message includes the identifier of the target NG-RAN node, and asource-to-target transparent container. The message also includesidentifier information indicating the AMF to which the target NG-RANnode is connected. The identifier information may be a tracking areaidentifier, a network sharding identifier, an AMF pool identifier, anAMF identifier or the like.

The message includes information of direct data forwarding pathavailability.

The source-to-target transparent container includes a PDU sessionidentifier, an identifier of the QoS flow in the PDU session, and thedownlink data forwarding proposed for the QoS flow. The eNB obtains thePDU session identifier corresponding to the EPS bearer and/or the QoSflow identifier in the PDU session through the PDN connectionestablishment process or through the handover process. It is alsopossible to obtain the QoS information of the mapped QoS flow. The eNBdetermines whether to propose data forwarding according to the E-RAB toPDU session or according to the mapping of the QoS flow in the E-RAB tothe PDU session and the QoS information, and the eNB may consider otherfactors such as whether there is buffered data to determine whether topropose data forwarding, without affecting the main content of theapplication.

Operation 402: the MME sends a forward relocation request message to theAMF. The MME selects and finds the AMF according to the identifierinformation of the AMF to which the target NG-RAN node is connected,which the information is included in the handover required message. Themessage includes the identifier of the target NG-RAN node, thesource-to-target transparent container and the UE context information.The UE context information includes UE mobile management (MM) contextinformation and a session management context. The message includes thehandover type.

The MME sends a direct forwarding indication to the AMF. The directforwarding indication may indicate direct data forwarding or indirectdata forwarding. If the MME doesn't receives direct data forwarding pathavailability from the source E-UTRAN, the MME determines whetherindirect data forwarding is possible. The MME informs the AMF of theinformation of whether direct data forwarding or indirect dataforwarding. The MME may also inform AMF of the information of dataforwarding being not possible. Data forwarding being not possible meansthat both direct data forwarding and indirect data forwarding are notpossible. Alternatively, the MME may also inform the AMF of theinformation of direct data forwarding path availability.

Operation 403 a: the AMF sends a creation session (SM) context requestmessage to the SMF. The AMF converts the received EPS UE context into a5GS UE context. The AMF may also exchange with the PCRF to obtain theconverted 5GS UE context. The AMF selects the SMF that serves the UE.

According to the information received in the forward relocation requestmessage, the AMF knows that the handover is a handover between differentsystems, and the AMF requests the SMF to provide the SM context. The AMFsends the message to each SMF serving the UE.

The AMF sends the direct forwarding indication to the SMF. The directforwarding indication may indicate direct data forwarding or indirectdata forwarding. The AMF informs the SMF the information that directdata forwarding or indirect data forwarding is available.

Operation 404: the SMF initiates an N4 session modification processbetween it and the UPF.

Operation 403 b: the SMF sends a creation session context responsemessage to the AMF. The message includes the SM context of the UE. TheSM context also includes a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer contexttogether with the SM context to the AMF at the same time when the AMFrequests the SM context. Alternatively, the SMF sends the mapped EPSbearer context to the AMF when the AMF requests the mapped EPS contextat the same time.

The 5GS UE context includes QoS information in the 5G system. The QoSinformation in the 5G system includes a QoS rule and/or a QoS profile.The AMF may map EPS QoS information into 5G QoS information, or the AMFinteracts with the 5G policy control function (5G-PCF) to derive 5G QoSinformation.

The SMF determines direct data forwarding, indirect data forwarding, ordata forwarding not possible. If the direct forwarding indicationreceived by the SMF indicates that direct data forwarding is available,the SMF determines to use direct data forwarding. If the directforwarding indication received by the SMF indicates indirect dataforwarding and that indirect data forwarding is possible, the SMFdetermines to use indirect data forwarding. If the direct forwardingindication received by the SMF indicates indirect data forwarding but noindirect data forwarding connectivity between source and target, the SMFdetermines that data forwarding is not possible. The SMF includesinformation of direct data forwarding, indirect data forwarding, or dataforwarding being not possible in the N2 session management (SM)information container. Direct data forwarding information may beinformation of direct data forwarding path availability. Data forwardingbeing not possible means that indirect data forwarding is not possibleor both direct and indirect data forwarding are not possible.

Operation 405: the AMF sends the handover request message to the NG-RAN.The message includes information of the PDU session to be established.The information of the PDU session includes a session identifier,session QoS information, QoS flow information, uplink tunnel informationfor each session, and/or a source-to-target transparent container. Themessage includes the type of handover.

The message includes the information of direct data forwarding, indirectdata forwarding, or data forwarding being not possible. The aboveinformation may be included in a N2 SM information container. Directdata forwarding information may be information of direct data forwardingpath availability. Data forwarding being not possible means thatindirect data forwarding is not feasible or both direct and indirectdata forwarding are not feasible.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the E-RAB identifiermapped by the QoS flow and/or the mapped QoS information.

Operation 406: the NG-RAN sends a handover request acknowledgementmessage to the AMF. The message includes one or more of the followinginformation:

1) the target-to-source transparent container. The target-to-sourcetransparent container may further include a mapping relationship betweena QoS flow and an EPS bearer in the PDU session, that is, the EPS beareridentifier mapped by the QoS flow and/or the mapped QoS information.

2) the established PDU session information list accepted by the NG-RAN.The PDU session information list includes a PDU session identifier,downlink tunnel information of the NG3 interface used for the PDUsession, QoS flow information accepted by the PDU session, andunaccepted QoS flow information.

If it is direct data forwarding, for a QoS flow accepted for dataforwarding or a E-RAB accepted for data forwarding by the NG-RAN, theNG-RAN allocates the downlink data forwarding tunnel information to therespective E-RAB, and the E-RAB identifier and the downlink tunnelinformation for the E-RAB allocated by the NG-RAN are included in thehandover request acknowledgement message. If it is indirect dataforwarding, for a QoS flow accepted for data forwarding by the NG-RAN,the NG-RAN allocates the downlink data forwarding tunnel information forthe PDU session to which the QoS flow belongs; the PDU sessionidentifier and the downlink tunnel information corresponding to PDUsession allocated by the NG-RAN are included in the handover requestacknowledgement message, and the QoS flow list accepted for dataforwarding may be further included in the handover requestacknowledgement message. If data forwarding is not possible, the NG-RANdoes not need to allocate data forwarding tunnel information.

3) the PDU session information list failed to be setup by the NG-RAN.The PDU session information list includes the PDU session identifier andthe reason for not accepting.

Operation 407: the AMF sends an update SM context request message to theSMF. If tunnel information for data forwarding is received from theNG-RAN, the AMF sends the data forwarding tunnel information receivedfrom the NG-RAN to the SMF. The AMF sends the tunnel informationreceived from the NG-RAN for data forwarding to the SMF. The AMF sendsthe information of whether it is direct data forwarding or indirect dataforwarding to the SMF. AMF may inform SMF of direct data forwarding orindirect data forwarding in an explicit manner. The AMF may also informthe SMF in an implicit manner, that is, if the SMF receives the dataforwarding tunnel information for each E-RAB, it is direct dataforwarding, and if the SMF receives the data forwarding tunnelinformation for each PDU session, it is indirect data forwarding, and ifno data forwarding tunnel information is received, data forwarding isnot feasible or data forwarding is not accepted by the target basestation. The message includes a PDU session to which the EPS bearerbelongs. The message may also include a mapping relationship between anEPS bearer and a QoS flow in the PDU session.

Operation 408: the SMF initiates a session modification process betweenit and the UPF. If the SMF receives the data forwarding tunnelinformation of each PDU session, the SMF sends the NG3 interfacedownlink data forwarding tunnel information allocated by the NG-RAN tothe UPF through the N4 session modification process, wherein the dataforwarding tunnel information corresponds to each PDU session. The SMFallocates the data forwarding tunnel information between the SGW and theUPF, or the UPF allocates the tunnel information for data forwardingbetween the SGW and the UPF and sends the tunnel information to the SMF,wherein the data forwarding tunnel information is for each E-RAB. The N4session modification message includes a PDU session to which the EPSbearer belongs. The N4 session establishment or N4 session modificationmessage may further include a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF receives the dataforwarding tunnel information for an E-RAB, it is direct dataforwarding, and the SMF or the UPF does not need to allocate dataforwarding tunnel information.

Operation 409: the SMF sends an update SM context response message tothe AMF. The SMF sends the tunnel information for data forwarding to theAMF. Corresponding to direct data forwarding, the SMF sends the tunnelinformation for each E-RAB received from the AMF to the AMF, and thetunnel information for each E-RAB is allocated by the target NG-RAN.Corresponding to indirect data forwarding, the SMF sends the tunnelinformation for each E-RAB allocated by the SMF or UPF to the AMF, andthe tunnel information is used for data forwarding between the SGW andthe UPF.

Operation 410: the AMF sends a forward relocation response message tothe MME. The message includes data forwarding tunnel information. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN. For indirect data forwarding, the tunnel information istunnel information received from the SMF for data forwarding between theSGW and the UPF. The message includes a target-to-source transparentcontainer.

Operation 411: the MME sends a creating indirect data forwarding tunnelrequest message to the SGW for indirect data forwarding, if the MMEreceives the tunnel information for data forwarding. The message is usedto send tunnel information for data forwarding between the SGW and theUPF to the SGW. The SGW sends a creating indirect data forwarding tunnelresponse message to the MME. The message includes uplink tunnelinformation allocated by the SGW for data forwarding over the S1interface. For direct data forwarding, this operation is not required tobe performed. The MME knows whether it is direct data forwarding orindirect data forwarding according to the information of directforwarding path availability received from the source base station, asdescribed in operation 402.

Operation 412: the MME sends a handover command message to the E-UTRAN.The message includes a target-to-source transparent container. Themessage includes the type of handover.

The message includes data forwarding tunnel information. For indirectdata forwarding, the tunnel information is allocated by the SGW. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN.

Operation 413: the E-UTRAN sends a handover command message to the UE.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the EPS bearer identifierand/or the mapped QoS information mapped by the QoS flow.

The E-UTRAN forwards data. For the E-RAB for which the data forwardingtunnel information is received, it indicates that the target basestation accepts data forwarding, and the E-UTRAN forwards the data tothe corresponding tunnel. For direct data forwarding, the target NG-RANdirectly receives the data forwarded by the E-UTRAN. For indirect dataforwarding, the SGW receives the data forwarded by the E-UTRAN. The SGWforwards the data to the UPF. The SGW forwards data to the UPF for eachEPS bearer accepted for data forwarding on the corresponding tunnel. TheUPF forwards the data to the NG-RAN. The UPF sends the data, belongingto the same PDU session, received from the SGW on the tunnel for eachEPS bearer to the NG-RAN through the corresponding PDU session tunnel,that is, the UPF performs mapping of multiple tunnels to one tunnel. TheUPF forwards data to the NG-RAN according to the session transmissionmanner in the 5GS, for example, through which several QoS flows to senddownlink data in each PDU session, and how to set the header of the QoSflow. The UPF adds a QoS flow identifier (QFI) to the packet headerforwarded to the target NG-RAN.

The NG-RAN receives the forwarded data from a PDU session tunnel, andthe NG-RAN sends the received data to the UE according to an existingmanner. The NG-RAN receives the forwarded data from an E-RAB tunnel, andthe NG-RAN directly sends the data to the PDCP layer of thecorresponding DRB with no need for SDAP layer processing. Based on themapping between an E-RAB ID(s) and a QoS Flow ID(s) received in thehandover request message, the NG-RAN knows the DRB corresponding to theE-RAB, and directly sends the received forwarded data to the PDCP entityof the corresponding DRB. The NG-RAN first sends the forwarded data tothe UE, and then sends the data received from a new NG-U to the UE.

During the establishment of the PDU session or the establishment of theEPS bearer, the UE receives the QoS information of the QoS flow mappedby the EPS bearer and/or the QoS flow information from the network. TheUE establishes the correspondence between the ongoing EPS bearer and theQoS flow included in the handover command message. For an EPS bearerthat does not have a corresponding QoS flow, the UE may delete it.

Alternatively, the UE obtains the mapping relationship between a QoSflow and an EPS bearer in the PDU session from the handover commandmessage. The UE establishes the correspondence between the ongoing EPSbearer and the QoS flow included in the handover command message. For anEPS bearer that does not have a corresponding QoS flow, the UE maydelete it.

Operation 414: the UE sends a handover complete message to the NG-RAN.

Operation 415: the NG-RAN sends a handover notify message to the AMF.The message includes the tunnel information allocated by the NG-RAN fordownlink data transmission.

Operation 416: the AMF sends an update SM context request message to theSMF.

Operation 417: the SMF sends a N4 session modification message to theUPF. The UPF sends the N4 session modification response message to theSMF.

The AMF sends the tunnel information allocated by the NG-RAN fordownlink data transmission to the UPF through the AMF.

Operation 418: the SMF sends an update SMF context response message tothe AMF.

As such, the description of the first embodiment of first handovermethod of the application is completed, and the problem of coexistenceof different data forwarding methods when the UE moves between the EPSand the 5G system is completely solved by the method, thereby avoidingdata loss, ensuring service continuity and interoperability of differentequipment from different vendors, and reducing configuration byoperator.

The second embodiment of the first method for supporting handoveraccording to the application is shown in FIG. 5.

FIG. 5 shows a schematic diagram of the second embodiment of the firstmethod for supporting handover according to an embodiment of thedisclosure.

Referring to FIG. 5, the method solves the above two problems, so thatdata forwarding in the handover process is successfully performed, anddifferent entities in the network work in coordination to ensuresuccessful data forwarding. Detailed descriptions of operationsunrelated to the embodiment are omitted herein. This embodiment is usedfor handover from 5GS to EPS, including operations of:

Operation 501: the NG-RAN determines to hand over the UE to the E-UTRAN.

The E-UTRAN herein may be an eNB connected to the EPC. The NG-RAN may bea gNB or a centralized unit CU in a gNB or an eNB connected to the 5GC.

The user plane path before handover is UPF to NG-RAN. The SGW needs tosupport an interface to connect with the UPF. The UPF may include thefunction of the PGW user plane to perform the function of the user planeanchor node during the handover between different RATs.

The UE has one or more PDU sessions in progress. Each PDU sessionincludes one or more QoS flows. In a PDU session establishment processor a guaranteed business rate (GBR) QoS flow establishment process, themapped EPS QoS information and/or the EPS bearer identifier areallocated for the QoS flow. The non-guaranteed business rate (non-GBR)QoS flow is mapped to a default EPS bearer. The GBR QoS flow is mappedto an EPS dedicated bearer. The EPS QoS information mapped to the QoSflow may be allocated by the PCC or SMF. The EPS bearer identifiermapped to the QoS flow may be allocated by the SMF or AMF. Forsupporting the handover between different systems, the SMF may have thefunction of the PGW control plane. In the scene of deploying the PCC,the policy control function (PCF) provides the EPS QoS mapped to QoSflow to the SMF. In order to support handover between different systems,the PCF may also have a policy control and charging rules function(PCRF). The SMF sends the EPS QoS information and/or EPS beareridentifier mapped to the QoS flow to the UE through the AMF, forexample, sending them through a non-access layer message PDU sessionestablishment message to the UE. During the PDU session establishment orguaranteed business rate (GBR) QoS flow establishment process, the SMFmay also send the EPS QoS information and/or E-RAB identifier mapped tothe QoS flow to the NG-RAN through the AMF. The AMF sends the EPS QoSinformation and/or E-RAB identifier mapped to the QoS flow to the NG-RANthrough an initial context establishment request message or a PDUsession resource establishment request message. The NG-RAN may send theEPS QoS information or E-RAB identifier mapped to the QoS flow to the UEthrough an RRC message. The E-RAB and EPS bearer are the same orone-to-one correspondence, which are referred to as an EPS bearer in thecore network, and are referred to as an E-RAB in the access network. TheE-RAB identifier and the EPS bearer identifier are the same orone-to-one correspondence, which are referred to as an EPS beareridentifier in the core network, and are referred to as an E-RABidentifier in the access network.

Operation 502: the NG-RAN sends the handover required message to theAMF. The message includes the identifier of the target eNB, asource-to-target transparent container. The source-to-target transparentcontainer includes an E-RAB identifier and downlink data forwardingproposed for the E-RAB. The NG-RAN obtains the EPS bearer identifiermapped to the QoS flow in the PDU session through the PDU sessionestablishment process or through the handover process, as well mayobtain the mapped EPS QoS information. The NG-RAN determines whether topropose data forwarding according to the mapping of QoS flow to E-RABand the QoS information, and the NG-RAN may consider other factors suchas whether there is buffered data to determine whether to propose dataforwarding, without affecting the main concept of the application. Themessage includes information of direct forwarding path availability.

The message further includes identifier information indicating the MMEto which the target eNB is connected. The identifier information may bea tracking area identifier or an MME identifier.

The message also includes the handover type.

The AMF determines whether direct data forwarding or indirect dataforwarding is available. If the AMF does not receive information ofdirect forwarding path availability from the source NG-RAN, the AMFdetermines whether indirect data forwarding is feasible. If direct dataforwarding is feasible, direct data forwarding is used.

Operation 503 a: the AMF sends a session management (SM) context requestmessage to the SMF. Based on the information received in the handoverrequired message, the AMF knows that the handover is a handover betweendifferent systems, and the AMF requests the SMF to provide the SMcontext. The AMF may also request an EPS bearer context. The AMF sendsthe message to each SMF serving the UE. The AMF sends a directforwarding indication or information of direct forwarding pathavailability to the SMF. The direct forwarding indication may indicatedirect data forwarding or indirect data forwarding. The AMF informs theSMF the information of whether direct data forwarding or indirect dataforwarding is available. The SMF saves the received information.

Operation 503 b: the SMF sends an N4 session modification requestmessage to the UPF. The message includes the direct forwardingindication or the information of direct forwarding path availability.The direct forwarding indication may indicate direct data forwarding orindirect data forwarding. The UPF saves the direct forwarding indicationor the information of whether direct data forwarding is feasible. TheUPF sends an N4 session modification response message to the SMF.

Operation 503 c: the SMF sends an SM context response message to theAMF. The message includes the SM context of the UE. The SM context alsoincludes the mapped EPS bearer context, such as EPS bearer identifierand/or the EPS QoS information. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer context alongwith the SM context to the AMF at the same time, when the AMF requeststhe SM context. Alternatively, the SMF sends the mapped EPS bearercontext to the AMF along with the SM context, only when the AMF requeststhe SM context and also requests the mapped EPS bearer context to theSMF.

SMF determines direct data forwarding, indirect data forwarding, or dataforwarding not possible. If the direct forwarding path availability isreceived by the SMF, the SMF determines to use direct data forwarding.If the SMF does not receive direct data forwarding path availability,the SMF determines whether indirect data forwarding is feasible. Ifindirect data forwarding is feasible, the SMF determines to use indirectdata forwarding. If the SMF does not receive direct data forwarding pathavailability and there is no indirect data forwarding connectivitybetween source and target, the SMF determines that data forwarding isnot possible.

The SMF sends information of direct data forwarding, indirect dataforwarding, or data forwarding being not possible, to the AMF. Directdata forwarding information may be information of direct data forwardingpath availability. Data forwarding being not possible means thatindirect data forwarding is not possible or both direct and indirectdata forwarding are not possible.

Operation 504: the AMF sends a forward relocation request message to theMME. The AMF selects and finds the MME according to the identifierinformation of the MME connected to the target eNB included in thehandover required message. The identifier information of the MMEconnected to the target eNB may be a TAI. The message includes anidentifier of the target eNB, a source-to-target transparent container,and the mapped EPS UE context information. The mapped EPS UE contextinformation includes UE mobile management (MM) context information andsession SM context information.

The AMF sends a direct forwarding indication to the MME.

If the AMF does not receive information of direct data forwarding pathavailability from the source NG-RAN, the AMF determines whether indirectdata forwarding is feasible. If direct data forwarding is feasible,direct data forwarding is used. If direct data forwarding is notfeasible, the AMF determines whether indirect data forwarding isfeasible. The AMF knows whether indirect data forwarding is feasiblebased on the information received from the SMF. The AMF knows whetherindirect data forwarding is feasible based on information of direct dataforwarding, indirect data forwarding, or data forwarding being notpossible, received from the SMF. The AMF informs the MME whether it isdirect data forwarding or indirect data forwarding. The AMF may alsoinform the MME of information of data forwarding being not possible.Data forwarding being not possible means that both direct dataforwarding and indirect data forwarding are not possible or indirectdata forwarding is not possible.

Operation 505: the MME sends a creation session request message to theSGW. The message includes EPS bearer context information.

Operation 506: the SGW sends a creation session response message to theMME. The message includes tunnel information for an S1 interface to senduplink data allocated by the SGW.

Operation 507: the MME sends a handover request message to the E-UTRAN.The message includes a source-to-target transparent container and E-EABcontext. The E-RAB context includes the E-RAB to be established anduplink tunnel information of the S1 interface allocated by the SGW. TheE-RAB context includes information of whether data forwarding ispossible. The message includes the handover type, and the specificcontent thereof is the same as that in Operation 902, which details arenot described herein again. The message includes information that dataforwarding is not possible. If the MME receives indirect data forwardinginformation from the AMF (e.g., direct data forwarding indicationindicates indirect data forwarding) but indirect data forwarding is notfeasible, the MME determines that data forwarding is not possible. Ifthe MME receives a direct data forwarding indication from the AMFindicating direct data forwarding or the MME receives from the AMF thatdirect data forwarding path availability, data forwarding is possible.

Operation 508: the E-UTRAN sends a handover request acknowledgementmessage to the MME. The message includes the established E-RAB list andthe E-RAB list failed to be established, as well as the target-to-sourcetransparent container. Corresponding to the established E-RAB, thetunnel information for downlink data transmission of the S1 interface isfurther included. Corresponding to the established E-RAB, if the sourcebase station proposes the downlink data forwarding, data forwarding ispossible and the target eNB accepts the downlink data forwarding, thetarget base station includes the tunnel information for data forwardingallocated by the E-UTRAN for each E-RAB accepted for downlink dataforwarding.

Operation 509: the MME requests the SGW to create an indirect dataforwarding tunnel. This operation is performed only when indirect dataforwarding is applied. If the MME receives indirect data forwardinginformation from the AMF and indirect data forwarding is feasible, theMME knows that it is indirect data forwarding. If the MME receives thedownlink tunnel information for data forwarding from the E-UTRAN, theMME requests the SGW to create an indirect data forwarding tunnel. TheMME sends the transport layer address and TEID allocated by the eNB fordata forwarding to the SGW. The transport layer address and TEIDcorrespond to each E-RAB.

The SGW sends an indirect data forwarding tunnel creation responsemessage to the MME. The message includes the information allocated bythe SGW for data forwarding between the SGW and the UPF. The informationused for data forwarding between the SGW and the UPF includes an E-RABidentifier and tunnel information used by the E-RAB for data forwarding.The tunnel information includes a transport layer address and a TEIDallocated by the SGW. The SGW allocates downlink data forwarding tunnelinformation for the E-RAB accepted for downlink data forwarding. The SGWallocates uplink data forwarding tunnel information for the E-RABaccepted for uplink data forwarding. The data forwarding tunnelinformation included in the E-RAB information may include uplink and/ordownlink data forwarding tunnel information.

Operation 509 is performed when indirect data forwarding is feasible.

Operation 510: the MME sends a forward relocation response message tothe AMF. The message includes tunnel information for data forwarding.For direct data forwarding, the data forwarding tunnel information isreceived from the target base station by the MME. For indirect dataforwarding, the tunnel information is allocated by the SGW and isreceived by the MME from the SGW. The tunnel information corresponds toeach EPS bearer. The tunnel information of data forwarding may includedownlink and/or uplink data forwarding tunnel information. The messageincludes a target-to-source transparent container.

The MME directly sends the E-RAB information to the AMF, and the AMFperforms the conversion.

Operation 511: the AMF sends an update SM context request message to theSMF. The AMF requests the SMF to create a data forwarding tunnel. Forindirect data forwarding, the AMF requests the SMF to create a dataforwarding tunnel. The message includes PDU session information. The PDUsession information includes a PDU session identifier, a QoS flowinformation included in the PDU session, the EPS bearers needing dataforwarding in the EPS system in each PDU session, a mapping relationshipbetween a QoS flow and an EPS bearer, an EPS bearer identifier and/orQoS information of the EPS bearer. The message includes tunnelinformation received from the MME for data forwarding. The AMF sends adirect forwarding indication to the SMF. The direct forwardingindication may indicate direct data forwarding or indirect dataforwarding. The AMF informs the SMF whether it is direct data forwardingor indirect data forwarding. This operation is mandatory for indirectdata forwarding. For direct data forwarding, operation 511 and operation513 may not be performed.

Operation 512 is performed for indirect data forwarding. For direct dataforwarding, operation 512 may not be performed. The SMF determineswhether to perform operation 512 according to the information receivedin operation 503 or according to direct data forwarding or indirect dataforwarding received from the AMF in this operation. Corresponding to themethod in which the SMF perform determination according to theinformation received in operation 503, if the SMF receives direct dataforwarding path availability, the SMF determines to use direct dataforwarding. If the SMF does not receive direct data forwarding pathavailability, the SMF determines whether indirect data forwarding isavailable. Thus, the SMF knows whether it is direct data forwarding orindirect data forwarding.

Operation 512: the SMF sends an N4 session modification message to theUPF. The message includes PDU session information. The PDU sessioninformation includes a PDU session identifier, a QoS flow informationincluded in the PDU session, the EPS bearers needing data forwarding inthe EPS system in each PDU session, a mapping relationship between a QoSflow and an EPS bearer, and an EPS bearer identifier and/or QoSinformation of the EPS bearer. The message includes tunnel informationreceived from the AMF for data forwarding.

The N4 session modification message includes EPS bearer informationincluded in the PDU session. The EPS bearer information includes an EPSbearer identifier and tunnel information used by the EPS bearer for dataforwarding. The SMF informs the UPF the correspondence between a QoSflow and an EPS bearer in the PDU session. The UPF knows the QoS flowinformation of the PDU session in the 5G system. The UPF receives theEPS bearer information and the mapping relationship between a QoS flowand an EPS bearer in the PDU session, from the SMF.

The SMF sends the information of the direct forwarding indication to theUPF. The direct forwarding indication may indicate direct dataforwarding or indirect data forwarding. The SMF informs the UPF whetherit is direct data forwarding or indirect data forwarding.

For indirect data forwarding, the SMF allocates tunnel information fordata forwarding between the NG-RAN and the UPF, or the UPF allocatestunnel information for data forwarding between the NG-RAN and the UPFand sends it to the SMF. For indirect data forwarding, the PDU sessiontunnel is used for data forwarding between the NG-RAN and the UPF. TheUPF allocates data forwarding tunnel information for the PDU sessioncorresponding to the EPS bearer accepted for data forwarding. The tunnelinformation includes a transport layer address and a TEID. The UPF sendsthe allocated tunnel information for data forwarding to the SMF. The SMFreceives the N4 session modification response message from the UPF. Themessage includes tunnel information allocated by the UPF for dataforwarding between the NG-RAN and the UPF. For direct data forwarding,the UPF does not need to allocate data forwarding tunnel information.According to the information received in operation 503 or in thisoperation, the UPF knows whether it is direct data forwarding orindirect data forwarding. For direct data forwarding, operation 512 mayalso not be performed.

Operation 513: the SMF sends an update SM context response message tothe AMF. For direct data forwarding, the message includes tunnelinformation for data forwarding, received by the SMF from the AMF. Thetunnel information is used for direct data forwarding, and is for eachEPS bearer. For indirect data forwarding, the message includes tunnelinformation allocated by the SMF or UPF for data forwarding between theNG-RAN and the UPF. The tunnel information is for each PDU session.

Operation 514: the AMF sends a handover command message to the NG-RAN.The message includes a target-to-source transparent container, tunnelinformation for data forwarding allocated by E-UTRAN or the UPF or SMF.The tunnel information for data forwarding is for each PDU session oreach E-RAB. For direct data forwarding, the tunnel information for dataforwarding is for each E-RAB for which data forwarding is accepted bythe target eNB. For indirect data forwarding, the tunnel information fordata forwarding is for each PDU session to which the QoS flow acceptedfor data forwarding belongs. The message further includes establishedPDU session information and PDU session information that is notsuccessfully established. The established PDU session informationincludes the established QoS flow information and the QoS flowinformation that is note successfully established.

Operation 515: the NG-RAN sends a handover command message to the UE.

The NG-RAN forwards the data.

If the NG-RAN receives the data forwarding tunnel information for eachPDU session, the NG-RAN forwards the data to the UPF. The NG-RANforwards data of QoS flows accepted for data forwarding to the UPF onthe tunnel the corresponding PDU session. The NG-RAN sends the data ofeach QoS flow to the UPF on the user plane tunnel allocated for the PDUsession. For the downlink data, the NG-RAN sends downlink packets to theUPF on the tunnel allocated for downlink data forwarding. The UPFforwards the data to the SGW. The UPF adds the QFI corresponding to theQoS flow to the packet header, and forwards the data received from theNG-RAN to the SGW through the user plane tunnel allocated for the mappedEPS bearer. The UPF forwards the data of different QoS flows in the PDUsession to the SGW through the user plane tunnel allocated for themapped EPS bearer according to the mapping relationship between a QoSflow and an EPS bearer. According to the mapping relationship between aQoS flow and an EPS bearer and the EPS bearer information accepted fordata forwarding, the UPF knows the QoS flow accepted for dataforwarding, and the UPF forwards the data of the QoS flow accepted fordata forwarding to the SGW through the user plane tunnel allocated forthe mapped EPS bearer. Corresponding to the QoS flow that not acceptedfor data forwarding, there is no corresponding data forwarding tunnel,and the UPF discards the data.

If the NG-RAN receives the tunnel information for each E-RAB, the NG-RANforwards the data of the QoS flows accepted for data forwarding to therespective E-RAB tunnel. The NG-RAN forwards the PDCP Service Data Unit(SDU) to the respective E-RAB tunnel. The PDCP SDU does not have asequence number (SN). For direct data forwarding, the data is sentdirectly to the target base station.

For indirect data forwarding, the SGW forwards the data to the E-UTRAN.The SGW sends the data received from the tunnel for each EPS bearer fromthe UPF to the E-UTRAN through the corresponding tunnel allocated by theE-UTRAN. The SGW forwards the data to the E-UTRAN according to thesession transmission mode in the EPS.

The E-UTRAN receives the forwarded data from the E-RAB tunnel, and theE-UTRAN first sends the forwarded data to the UE, and then sends thedata received from the new S1-U to the UE.

During the establishment of the PDU session or the establishment of theGBR QoS flow, the UE receives the EPS QoS information and/or the EPSbearer identifier information mapped to the QoS flow from the network.The UE associates the ongoing QoS flow and the EPS bearer identifierincluded in the handover command message to establish a correspondencetherebetween. For the QoS flow without corresponding to EPS bearer, theUE may delete it.

Operation 516: the UE sends a handover complete message to the E-UTRAN.

Operation 517: the E-UTRAN sends a handover notify message to the MME.The message includes tunnel information allocated by the E-UTRAN fordownlink data transmission.

Operation 518: the MME sends a modification bearer request message tothe SGW. The message includes tunnel information used by the 51interface for downlink data transmission.

Operation 519: the SGW sends a modification bearer request message tothe SMF. The SMF may further have the function of the PGW control plane.The SGW allocates tunnel information for downlink data transmissionbetween the SGW and the UPF, wherein the tunnel information correspondsto each EPS bearer or each PDU session.

Operation 520: the SMF request a UPF session modification. The SMF mayfurther have the function of the PGW control plane. The SMF sends thetunnel information for the downlink data transmission between the SGWand the UPF allocated by the SGW to the UPF, wherein the tunnelinformation corresponds to each EPS bearer or each PDU session. The UPFsends a session modification response to the SMF. The UPF allocatestunnel information for uplink data transmission between the SGW and theUPF, and the UPF sends the tunnel information for the uplink datatransmission to the SMF.

Operation 521: the SMF sends a modification bearer response message tothe SGW. The message includes tunnel information for uplink datatransmission between the SGW and the UPF, which the information isallocated by the UPF.

Operation 522: the SGW sends a modification bearer response message tothe MME.

As such, the description of the second embodiment of the first handovermethod of the application is completed, and the problem of coexistenceof different data forwarding methods when the UE moves between the EPSand the 5GS system is completely solved by the method, thereby avoidingdata loss, ensuring service continuity and interoperability of differentequipment from different vendors, and reducing configuration byoperator.

The second method for supporting handover according to the applicationis shown in FIG. 6.

FIG. 6 shows a schematic diagram of a second method for supportinghandover according to an embodiment of the disclosure.

Referring to FIG. 6, in the method, the source base station informs thetarget base station of the identifier of the source base station or theidentifier of the source cell through the core network, and the targetbase station determines whether direct data forwarding is available, sothat the target base station determines how to allocate the dataforwarding tunnel information. The method solves the above two problems,so that data forwarding in the handover process is successfullyperformed, and different entities in the network work in coordination toensure successful data forwarding. Detailed descriptions of operationsunrelated to the embodiment are omitted herein. The method includes theoperations of:

Operation 600: the E-UTRAN determines to hand over the UE to the NG-RAN.

The E-UTRAN herein may be an eNB connected to the EPC. The NG-RAN may bea gNB or a centralized unit CU in a gNB or an eNB connected to the 5GC.An eNB connected to the 5GC may also be referred to as an ng-eNB.

The user plane path before the handover is PGW-U+UPF (the UPF having thefunction of the PGW user plane, hereinafter referred to as UPF) and theSGW to the E-UTRAN. The SGW needs to support the interface to connectwith PGW-U+UPF. The UE has one or more PDU sessions in progress. EachPDU session includes one or more EPS bearers. In a PDU sessionestablishment process or an EPS bearer establishment process, the mappedQoS information and/or the QoS flow identifier of the QoS flow areallocated for the EPS bearer. The default EPS bearer is mapped to anon-guaranteed business rate (non-GBR) QoS flow. The QoS informationand/or the QoS flow identifier of the QoS flow mapped to the EPS bearermay be allocated by the function of the PCC or the PGW control plane. Inorder to support handover between different systems, the function of thePGW control plane may further have an SMF function. In the scene ofdeploying the PCC, the policy control and charging rules function (PCRF)provides the QoS information and/or QoS flow identifier of the QoS flowmapped to the EPS bearer to the SMF. In order to support handoverbetween different systems, the PCRF may also have a policy controlfunction (PCF). The SMF sends the QoS information and/or QoS identifierof the QoS flow mapped to the EPS bearer to the UE through the MME, forexample, sending them to the UE through a non-access layer message PDNconnection establishment message. During the PDU session establishmentprocess or the EPS bearer establishment process, the SMF may also sendthe QoS information and/or QoS flow identifier of the QoS flow mapped tothe EPS bearer to the E-UTRAN through the MME. The E-UTRAN may send themapping information to the UE through an RRC message. The E-RAB and EPSbearer identifiers are the same or one-to-one correspondence, which arereferred to as an EPS bearer in the core network, and are referred to asan E-RAB in the access network. The E-RAB identifier and the EPS beareridentifier are the same or one-to-one correspondence, which are referredto as an EPS bearer identifier in the core network, and are referred toas an E-RAB identifier in the access network.

Operation 601: the E-UTRAN sends a handover required message to the MME.The message includes the identifier of the target NG-RAN node, and asource-to-target transparent container. The message also includesidentifier information indicating the AMF to which the target NG-RANnode is connected. The identifier information may be a tracking areaidentifier, a network sharding identifier, an AMF pool identifier, anAMF identifier or the like.

The message includes information of direct forwarding path availability.

The message includes an identifier of the source base station or anidentifier of the source cell. The information may be included in thesource-to-target transparent container or directly included in thehandover required message.

The source-to-target transparent container includes a PDU sessionidentifier, an identifier of the QoS flow in the PDU session, and thedownlink data forwarding proposed for the QoS flow. The eNB obtains thePDU session identifier corresponding to the EPS bearer and/or the QoSflow identifier in the PDU session through the PDN connectionestablishment process or through the handover process. It is alsopossible to obtain the QoS information of the mapped QoS flow. The eNBdetermines whether to propose data forwarding according to the E-RAB toPDU session or according to the mapping of the QoS flow in the E-RAB tothe PDU session and the QoS information, and the eNB may consider otherfactors such as whether there is buffered data to determine whether topropose data forwarding, without affecting the main content of theapplication.

Operation 602: the MME sends a forward relocation request message to theAMF. The MME selects and finds the AMF according to the identifierinformation of the AMF to which the target NG-RAN node is connected,which the information is included in the handover required message. Themessage includes the identifier of the target NG-RAN node, thesource-to-target transparent container and the UE context information.The UE context information includes UE mobile management (MM) contextinformation and a session management context. The message includes thehandover type. The message includes an identifier of the source basestation or an identifier of the source cell. The information may beincluded in the source-to-target transparent container or directlyincluded in the forward relocation request message.

The MME sends a direct forwarding indication to the AMF. If the MMEdoesn't receives direct data forwarding path availability from thesource E-UTRAN, the MME determines whether indirect data forwarding ispossible. The MME informs the AMF of the information of whether directdata forwarding or indirect data forwarding. The MME may also inform AMFof the information of data forwarding being not possible. Dataforwarding being not possible means that both direct data forwarding andindirect data forwarding are not possible. Alternatively, the MME mayalso inform the AMF of the information of direct data forwarding path isavailable.

The MME determines whether indirect data forwarding is possible. The MMEinforms the information of whether indirect data forwarding is possibleto the AMF. Data forwarding being not possible means that indirect dataforwarding is not possible.

Operation 603 a: the AMF sends a creation session (SM) context requestmessage to the SMF. The AMF converts the received EPS UE context into a5GS UE context. The AMF may also exchange with the PCRF to obtain theconverted 5GS UE context. The AMF selects the SMF that serves the UE.

According to the information received in the forward relocation requestmessage, the AMF knows that the handover is a handover between differentsystems, and the AMF requests the SMF to provide the SM context. The AMFsends the message to each SMF serving the UE.

The AMF sends the direct forwarding indication or direct data forwardingbeing available to the SMF, and the AMF informs the SMF of theinformation that direct data forwarding or indirect data forwarding isavailable.

Operation 604: the SMF initial an N4 session modification processbetween it and the UPF. The SMF sends a direct forwarding indication tothe UPF, and the SMF informs the UPF of the information that direct dataforwarding or indirect data forwarding is available. The SMF may alsoinform the UPF of the information that direct data forwarding isavailable.

Operation 603 b: the SMF sends a creation session context responsemessage to the AMF. The message includes the SM context of the UE. TheSM context also includes a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer contexttogether with the SM context to the AMF at the same time when the AMFrequests the SM context. Alternatively, the SMF sends the mapped EPSbearer context to the AMF when the AMF requests the mapped EPS contextat the same time.

The 5GS UE context includes QoS information in the 5G system. The QoSinformation in the 5G system includes a QoS rule and/or a QoS profile.The AMF may map EPS QoS information into 5G QoS information, or the AMFinteract with the 5G policy control function (5G-PCF) to derive 5G QoSinformation.

The SMF determines direct data forwarding, indirect data forwarding, ordata forwarding not possible. If the direct forwarding indicationreceived by the SMF indicates that direct data forwarding is available,the SMF determines to use direct data forwarding. If the directforwarding indication received by the SMF indicates indirect dataforwarding and that indirect data forwarding is possible, the SMFdetermines to use indirect data forwarding. If the direct forwardingindication received by the SMF indicates indirect data forwarding but noindirect data forwarding connectivity between source and target, the SMFdetermines that data forwarding is not possible. The SMF includesinformation of direct data forwarding, indirect data forwarding, or dataforwarding being not possible in the N2 session management (SM)information container. Or,

the SMF determines that indirect data forwarding or data forwarding isnot feasible. The SMF informs the target NG-RAN of the information. Or,

the SMF determines whether indirect data forwarding is not possible. TheSMF informs the target NG-RAN of the information that indirect dataforwarding is not possible and whether direct data forwarding isavailable.

Operation 605: the AMF sends the handover request message to the NG-RAN.The message includes information of the PDU session to be established.The information of the PDU session includes a session identifier,session QoS information, QoS flow information, uplink tunnel informationfor each session, and/or a source-to-target transparent container. Themessage includes the type of handover. The message includes anidentifier of the source base station or an identifier of the sourcecell. The identifier of the source base station may be sent to thetarget base station by using a source-to-target transparent container,or may be sent to the target base station by using the handover requiredof operation 601, the forwarding relocation request of operation 602,and the handover request message of this operation.

The message includes information that data forwarding is not possible.That data forwarding is not possible means that indirect data forwardingis not possible, or both direct data forwarding and indirect dataforwarding are not possible. The message may also include informationthat direct data forwarding is available. The above information may beincluded in a N2 SM information container.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the E-RAB identifiermapped by the QoS flow and/or the mapped QoS information.

Operation 606: the NG-RAN sends a handover request acknowledgementmessage to the AMF. The message includes one or more of the followinginformation:

1) the target-to-source transparent container. The target-to-sourcetransparent container may further include a mapping relationship betweena QoS flow and an EPS bearer in the PDU session, that is, the EPS beareridentifier mapped by the QoS flow and/or the mapped QoS information.

2) the established PDU session information list accepted by the NG-RAN.The PDU session information list includes a PDU session identifier,downlink tunnel information of the NG3 interface used for the PDUsession, QoS flow information accepted by the PDU session, andunaccepted QoS flow information.

If the NG-RAN does not receive that data forwarding is not possible, thetarget NG-RAN determines whether direct data forwarding is feasibleaccording to the received identifier of the source base station or theidentifier of the source cell, thereby determining whether to use directdata forwarding or indirect data forwarding. Direct data forwarding isused if direct data forwarding is feasible, and indirect data forwardingis used if direct data forwarding is not feasible. If the NG-RANreceives that data forwarding is not possible, the NG-RAN does notallocate a data forwarding tunnel identifier.

Another method for the NG-RAN to determine whether to use direct dataforwarding or indirect data forwarding is that: data forwarding beingnot possible received from the AMF means that indirect data forwardingis not possible, and the target NG-RAN judges whether direct dataforwarding is feasible according to the received identifier of thesource base station or the identifier of the source cell; direct dataforwarding is used if direct data forwarding is feasible, and indirectdata forwarding is used if direct data forwarding is not feasible andindirect data forwarding being not possible is not received. If directdata forwarding is not feasible and indirect data forwarding being notpossible is received at the same time, the NG-RAN does not allocate adata forwarding tunnel identifier.

Another method for the NG-RAN to determine whether to use direct dataforwarding or indirect data forwarding is that: data forwarding beingnot possible received from the AMF means that indirect data forwardingis not possible, the target NG-RAN determines whether to use direct dataforwarding or indirect data forwarding according to the receivedinformation that direct data forwarding is available; direct dataforwarding is used if direct data forwarding is available, and indirectdata forwarding is used if direct data forwarding is not feasible andindirect data forwarding being not possible is not received. If directdata forwarding is not feasible and indirect data forwarding being notfeasible is received, the NG-RAN does not allocate a data forwardingtunnel identifier.

Another method for the NG-RAN to determine whether to use direct dataforwarding or indirect data forwarding is that: if the NG-RAN does notreceive that data forwarding is not possible, the target NG-RANdetermines whether to use direct data forwarding or indirect dataforwarding according to the received information that direct dataforwarding is available; direct data forwarding is used if direct dataforwarding is available, and indirect data forwarding is used if directdata forwarding is not feasible. If data forwarding is not feasible, theNG-RAN does not allocate a data forwarding tunnel identifier.

If it is direct data forwarding, for a QoS flow accepted for dataforwarding or a E-RAB accepted for data forwarding by the NG-RAN, theNG-RAN allocates the downlink data forwarding tunnel information to therespective E-RAB, and the E-RAB identifier and the downlink tunnelinformation for the E-RAB allocated by the NG-RAN are included in thehandover request acknowledgement message. If it is indirect dataforwarding, for the QoS flow accepted for data forwarding by the NG-RAN,the NG-RAN allocates the downlink data forwarding tunnel information forthe PDU session to which the QoS flow belongs; the PDU sessionidentifier and the downlink tunnel information corresponding to PDUsession allocated by the NG-RAN are included in the handover requestacknowledgement message, and the QoS flow list accepted for dataforwarding may be further included in the handover requestacknowledgement message. If data forwarding is not feasible, the NG-RANdoes not need to allocate data forwarding tunnel information.

3) the PDU session information list failed to be setup by the NG-RAN.The PDU session information list includes the PDU session identifier andthe reason for not accepting.

The message includes information of direct data forwarding or indirectdata forwarding. The information may be explicit or implicit. Theimplicit manner is that, if the data forwarding tunnel informationincluded in the message corresponds to each E-RAB, it is direct dataforwarding, and if the data forwarding tunnel information included inthe message corresponds to each PDU session, it is indirect dataforwarding.

Operation 607: the AMF sends an update SM context request message to theSMF. If tunnel information for data forwarding is received from theNG-RAN, the AMF sends the data forwarding tunnel information receivedfrom the NG-RAN to the SMF. The AMF sends the tunnel informationreceived from the NG-RAN for data forwarding to the SMF. The AMF sendsthe information of whether it is direct data forwarding or indirect dataforwarding to the SMF. AMF may inform SMF of direct data forwarding,indirect data forwarding or data forwarding in an explicit manner. TheAMF may also inform the SMF in an implicit manner, that is, if the SMFreceives the data forwarding tunnel information for each E-RAB, it isdirect data forwarding, and if the SMF receives the data forwardingtunnel information for each PDU session, it is indirect data forwarding,and if no data forwarding tunnel information is received, dataforwarding is not feasible or data forwarding is not accepted by thetarget base station. The message includes a PDU session to which the EPSbearer belongs. The message may also include a mapping relationshipbetween an EPS bearer and a QoS flow in the PDU session.

Operation 608: the SMF initiates a session modification process betweenit and the UPF. If the SMF receives the data forwarding tunnelinformation of each PDU session, the SMF sends the NG3 interfacedownlink data forwarding tunnel information allocated by the NG-RAN tothe UPF through the N4 session modification process, wherein the dataforwarding tunnel information corresponds to each PDU session. The SMFallocates the data forwarding tunnel information between the SGW and theUPF, or the UPF allocates the tunnel information for data forwardingbetween the SGW and the UPF and sends the tunnel information to the SMF,wherein the data forwarding tunnel information is for each E-RAB. The N4session modification message includes a PDU session to which the EPSbearer belongs. The N4 session establishment or N4 session modificationmessage may further include a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF receives the dataforwarding tunnel information for an E-RAB, it is direct dataforwarding, and the SMF or the UPF does not need to allocate dataforwarding tunnel information.

Operation 609: the SMF sends an update SM context response message tothe AMF. The SMF sends the tunnel information for data forwarding to theAMF. Corresponding to direct data forwarding, the SMF sends the tunnelinformation for each E-RAB received from the AMF to the AMF, and thetunnel information for each E-RAB is allocated by the target NG-RAN.Corresponding to indirect data forwarding, the SMF sends the tunnelinformation for each E-RAB allocated by the SMF or UPF to the AMF, andthe tunnel information is used for data forwarding between the SGW andthe UPF.

The update SM context response message includes information of whetherit is direct data forwarding or indirect data forwarding.

Operation 610: the AMF sends a forward relocation response message tothe MME. The message includes data forwarding tunnel information. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN. For indirect data forwarding, the tunnel information istunnel information received from the SMF for data forwarding between theSGW and the UPF. The message includes a target-to-source transparentcontainer. The forward relocation response message includes informationof whether it is direct data forwarding or indirect data forwarding.

Operation 611: the MME sends a creating indirect data forwarding tunnelrequest message to the SGW for indirect data forwarding, if the MMEreceives the tunnel information for data forwarding. The message is usedto send tunnel information for data forwarding between the SGW and theUPF to the SGW. The SGW sends a creating indirect data forwarding tunnelresponse message to the MME. The message includes uplink tunnelinformation allocated by the SGW for data forwarding over the S1interface. For direct data forwarding, this operation is not required tobe performed. The MME knows whether it is direct data forwarding orindirect data forwarding according to the information of directforwarding path availability received from the source base station orinformation of whether it is direct data forwarding or indirect dataforwarding received from the AMF.

Operation 612: the MME sends a handover command message to the E-UTRAN.The message includes a target-to-source transparent container. Themessage includes the type of handover.

The message includes data forwarding tunnel information. For indirectdata forwarding, the tunnel information is allocated by the SGW. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN.

Operation 613: the E-UTRAN sends a handover command message to the UE.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the EPS bearer identifierand/or the mapped QoS information mapped by the QoS flow.

The E-UTRAN forwards data. For the E-RAB for which the data forwardingtunnel information is received, it indicates that the target basestation accepts data forwarding, and the E-UTRAN forwards the data tothe corresponding tunnel. For direct data forwarding, the target NG-RANdirectly receives the data forwarded by the E-UTRAN. For indirect dataforwarding, the SGW receives the data forwarded by the E-UTRAN. The SGWforwards the data to the UPF. The SGW forwards data to the UPF for eachEPS bearer accepted for data forwarding on the corresponding tunnel. TheUPF forwards the data to the NG-RAN. The UPF sends the data, belongingto the same PDU session, received from the SGW on the tunnel for eachEPS bearer to the NG-RAN through the corresponding PDU session tunnel,that is, the UPF performs mapping of multiple tunnels to one tunnel. TheUPF forwards data to the NG-RAN according to the session transmissionmanner in the 5GS, for example, through which several QoS flows to senddownlink data in each PDU session, and how to set the header of the QoSflow. The UPF adds a QoS flow identifier (QFI) to the packet headerforwarded to the target NG-RAN.

The NG-RAN receives the forwarded data from a PDU session tunnel, andthe NG-RAN sends the received data to the UE according to an existingmanner. The NG-RAN receives the forwarded data from an E-RAB tunnel, andthe NG-RAN directly sends the data to the PDCP layer of thecorresponding DRB with no need for SDAP layer processing. Based on themapping relationship between an E-RAB ID(s) and a QoS Flow ID(s)received in the handover request message, the NG-RAN knows the DRBcorresponding to the E-RAB, and directly sends the received forwardeddata to the PDCP entity of the corresponding DRB. The NG-RAN first sendsthe forwarded data to the UE, and then sends the data received from anew NG-U to the UE.

During the establishment of the PDU session or the establishment of theEPS bearer, the UE receives the QoS information of the QoS flow mappedby the EPS bearer and/or the QoS flow information from the network. TheUE establishes the correspondence between the ongoing EPS bearer and theQoS flow included in the handover command message. For an EPS bearerthat does not have a corresponding QoS flow, the UE may delete it.

Alternatively, the UE obtains the mapping relationship between a QoSflow and an EPS bearer in the PDU session from the handover commandmessage. The UE establishes the correspondence between the ongoing EPSbearer and the QoS flow included in the handover command message. For anEPS bearer that does not have a corresponding QoS flow, the UE maydelete it.

Operation 614: the UE sends a handover complete message to the NG-RAN.

Operation 615: the NG-RAN sends a handover notify message to the AMF.The message includes the tunnel information allocated by the NG-RAN fordownlink data transmission.

Operation 616: the AMF sends an update SM context request message to theSMF.

Operation 617: the SMF sends a N4 session modification message to theUPF. The UPF sends the N4 session modification response message to theSMF.

The AMF sends the tunnel information allocated by the NG-RAN fordownlink data transmission to the UPF through the AMF.

Operation 618: the SMF sends an update SMF context response message tothe AMF.

As such, the description of the second handover method of theapplication is completed, and the problem of coexistence of differentdata forwarding methods when the UE moves between the EPS and the 5Gsystem is completely solved by the method, thereby avoiding data loss,ensuring service continuity and interoperability of different equipmentfrom different vendors, and reducing configuration by operator.

The third method for supporting handover according to the application isshown in FIG. 7.

FIG. 7 shows a schematic diagram of a third method for supportinghandover according to an embodiment of the disclosure.

Referring to FIG. 7, the method is applicable to the second manner inwhich two data forwarding methods coexist, that is, which the dataforwarding method is specifically supported depends on theimplementation of the NG-RAN node and the UPF. This method is used forhandover from 5GS to EPS. Detailed descriptions of operations unrelatedto the embodiment are omitted herein. The method includes the operationsof:

Operation 701: the NG-RAN determines to hand over the UE to the E-UTRAN.

The E-UTRAN herein may be an eNB connected to the EPC. The NG-RAN may bea gNB or a centralized unit CU in a gNB or an eNB connected to the 5GC.

The user plane path before handover is UPF to NG-RAN. The SGW needs tosupport an interface to connect with the UPF. The UPF may include thefunction of the PGW user plane to perform the function of the user planeanchor node during the handover between different RATs.

The UE has one or more PDU sessions in progress. Each PDU sessionincludes one or more QoS flows. In a PDU session establishment processor a guaranteed business rate (GBR) QoS flow establishment process, themapped EPS QoS information and/or the EPS bearer identifier areallocated for the QoS flow. The non-guaranteed business rate (non-GBR)QoS flow is mapped to a default EPS bearer. The GBR QoS flow is mappedto an EPS dedicated bearer. The EPS QoS information mapped to the QoSflow may be allocated by the PCC or SMF. The EPS bearer identifiermapped to the QoS flow may be allocated by the SMF or AMF. Forsupporting the handover between different systems, the SMF may have thefunction of the PGW control plane. In the scene of deploying the PCC,the policy control function (PCF) provides the EPS QoS mapped to QoSflow to the SMF. In order to support handover between different systems,the PCF may also have a policy control and charging rules function(PCRF). The SMF sends the EPS QoS information and/or EPS beareridentifier mapped to the QoS flow to the UE through the AMF, forexample, sending them through a non-access layer message PDU sessionestablishment message to the UE. During the PDU session establishment orguaranteed business rate (GBR) QoS flow establishment process, the SMFmay also send the EPS QoS information and/or E-RAB identifier mapped tothe QoS flow to the NG-RAN through the AMF. The AMF sends the EPS QoSinformation and/or E-RAB identifier mapped to the QoS flow to the NG-RANthrough an initial context establishment request message or a PDUsession resource establishment request message. The NG-RAN may send theEPS QoS information and/or E-RAB identifier mapped to the QoS flow tothe UE through an RRC message. The E-RAB and EPS bearer are the same orone-to-one correspondence, which are referred to as an EPS bearer in thecore network, and are referred to as an E-RAB in the access network. TheE-RAB identifier and the EPS bearer identifier are the same orone-to-one correspondence, which are referred to as an EPS beareridentifier in the core network, and are referred to as an E-RABidentifier in the access network.

Operation 702: the NG-RAN sends the handover required message to theAMF. The message includes the identifier of the target eNB, asource-to-target transparent container. The source-to-target transparentcontainer includes an E-RAB identifier and downlink data forwardingproposed for the E-RAB. The NG-RAN obtains the EPS bearer identifiermapped to the QoS flow in the PDU session through the PDU sessionestablishment process or through the handover process, as well mayobtain the mapped EPS QoS information. The NG-RAN determines whether topropose data forwarding according to the mapping of QoS flow to E-RABand the QoS information, and the NG-RAN may consider other factors suchas whether there is buffered data to determine whether to propose dataforwarding, without affecting the main concept of the application. Themessage also includes that source NG-RAN node supports data forwardingof the PDU session tunnel and/or data forwarding of the E-RAB tunnel.The message includes the information of direct data forwarding pathavailability. Direct data forwarding may also implicitly inform the AMFthat data forwarding of the E-RAB tunnel is supported by the sourceNG-RAN.

Herein, the AMF obtains, through a UE-specific message, the dataforwarding method supported by the NG-RAN node. Another method for theAMF to obtain the NG-RAN node supporting data forwarding of the PDUsession tunnel and/or data forwarding of the E-RAB tunnel is through acommon process (non-UE-specific process), i.e. AMF obtains the dataforwarding method supported by the NG-RAN through the NG establishmentprocess. Corresponding to this method, the information of NG-RAN nodesupporting data forwarding of the PDU session tunnel and/or dataforwarding of the E-RAB tunnel is included in the NG establishmentrequest message sent by the NG-RAN to the AMF. The AMF saves thereceived information and uses the information when needing to hand overthe UE out of the NG-RAN node. The AMF sends an NG establishmentresponse message to the NG-RAN node.

The message further includes identifier information indicating the MMEto which the target eNB is connected. The identifier information may bea tracking area identifier or an MME identifier.

The message also includes the handover type.

Operation 703 a: the AMF sends a session management (SM) context requestmessage to the SMF. Based on the information received in the handoverrequired message, the AMF knows that the handover is a handover betweendifferent systems, and the AMF requests the SMF to provide the SMcontext. The AMF may also request an EPS bearer context. The AMF sendsthe message to each SMF serving the UE. The message also includes thatsource NG-RAN node supports data forwarding of the PDU session tunneland/or data forwarding of the E-RAB tunnel. The message includesinformation of direct data forwarding path availability. Direct dataforwarding may also implicitly inform the SMF that data forwarding ofthe E-RAB tunnel is supported by the source NG-RAN.

Operation 703 b: the SMF sends an N4 session modification requestmessage to the UPF. The message also includes that source NG-RAN nodesupports data forwarding of the PDU session tunnel and/or dataforwarding of the E-RAB tunnel. The message includes the information ofdirect data forwarding path availability. Direct data forwarding mayalso implicitly inform the UPF that data forwarding of the E-RAB tunnelis supported by the source NG-RAN. The UPF sends the N4 sessionmodification response message to the SMF.

Operation 703 c: the SMF sends an SM context response message to theAMF. The message includes the SM context of the UE. The SM context alsoincludes the mapped EPS bearer context, such as EPS bearer identifierand/or the EPS QoS information. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer context alongwith the SM context to the AMF at the same time when the AMF requeststhe SM context. Alternatively, the SMF sends the mapped EPS bearercontext to the AMF along with the SM context, only when the AMF requeststhe SM context and also requests the mapped EPS bearer context to theSMF.

Operation 704: the AMF sends a forward relocation request message to theMME. The AMF selects and finds the MME according to the identifierinformation of the MME connected to the target eNB included in thehandover required message. The identifier information of the MMEconnected to the target eNB may be a TAI. The message includes anidentifier of the target eNB, a source-to-target transparent container,and the mapped EPS UE context information. The mapped EPS UE contextinformation includes UE mobile management (MM) context information andsession SM context information.

If the AMF does not receive information of direct data forwarding pathavailability from the source NG-RAN, the AMF determines whether indirectdata forwarding is feasible. If direct data forwarding is feasible,direct data forwarding is used. Or, if direct data forwarding isfeasible and the source base station supports data forwarding of E-RABtunnel, direct data forwarding is used. The AMF informs the MME whetherdirect data forwarding, indirect data forwarding, or data forwarding isnot possible.

Operation 705: the MME sends a creation session request message to theSGW. The message includes EPS bearer context information.

Operation 706: the SGW sends a creation session response message to theMME. The message includes tunnel information for an S1 interface to senduplink data allocated by the SGW.

Operation 707: the MME sends a handover request message to the E-UTRAN.The message includes a source-to-target transparent container and E-EABcontext. The E-RAB context includes the E-RAB to be established anduplink tunnel information of the S1 interface allocated by the SGW. TheE-RAB context includes information of whether data forwarding ispossible. The message includes the handover type, and the specificcontent thereof is the same as that in operation 702, which details arenot described herein again.

Operation 708: the E-UTRAN sends a handover request acknowledgementmessage to the MME. The message includes the established E-RAB list andthe E-RAB list failed to be established, as well as the target-to-sourcetransparent container. Corresponding to the established E-RAB, thetunnel information for downlink data transmission of the S1 interface isfurther included. Corresponding to the established E-RAB, if the sourcebase station proposes the downlink data forwarding, data forwarding ispossible and the target eNB accepts the downlink data forwarding, thetarget base station includes the tunnel information for data forwardingof the S1 interface allocated by the E-UTRAN for each E-RAB accepted fordownlink data forwarding.

Operation 709: the MME requests the SGW to create an indirect dataforwarding tunnel. This operation is performed only when indirect dataforwarding is applied. If the MME receives the downlink tunnelinformation for data forwarding of the S1 interface from the E-UTRAN,the MME requests the SGW to create an indirect data forwarding tunnel.The MME sends the transport layer address and TEID allocated by the eNBfor data forwarding to the SGW. The transport layer address and TEIDcorrespond to each E-RAB.

The SGW sends an indirect data forwarding tunnel creation responsemessage to the MME. The message includes the information allocated bythe SGW for data forwarding between the SGW and the UPF. The informationused for data forwarding between the SGW and the UPF includes an E-RABidentifier and tunnel information used by the E-RAB for data forwarding.The tunnel information includes a transport layer address and a TEIDallocated by the SGW. The SGW allocates downlink data forwarding tunnelinformation for the E-RAB accepted for downlink data forwarding. The SGWallocates uplink data forwarding tunnel information for the E-RABaccepted for uplink data forwarding. The data forwarding tunnelinformation included in the E-RAB information may include uplink and/ordownlink data forwarding tunnel information.

Operation 709 is performed when indirect data forwarding is feasible.

Operation 710: the MME sends a forward relocation response message tothe AMF. The message includes tunnel information for data forwarding.For direct data forwarding, the data forwarding tunnel information isreceived from the target base station by the MME. For indirect dataforwarding, the tunnel information is allocated by the SGW and isreceived by the MME from the SGW. The tunnel information corresponds toeach EPS bearer. The tunnel information of data forwarding may includedownlink and/or uplink data forwarding tunnel information. The messageincludes a target-to-source transparent container.

The MME directly sends the E-RAB information to the AMF, and the AMFperforms the conversion.

Operation 711: the AMF sends an update SM context request message to theSMF. The message includes the information of direct data forwarding orindirect data forwarding. The AMF requests the SMF to create a dataforwarding tunnel. For indirect data forwarding, the AMF requests theSMF to create a data forwarding tunnel. The message includes PDU sessioninformation. The PDU session information includes a PDU sessionidentifier, a QoS flow information included in the PDU session, the EPSbearers needing data forwarding in the EPS system in each PDU session, amapping relationship between a QoS flow and an EPS bearer, an EPS beareridentifier and/or QoS information of the EPS bearer. The messageincludes information received from the MME for data forwarding. Themessage also includes that the source NG-RAN node supports dataforwarding of the PDU session tunnel and/or data forwarding of the E-RABtunnel.

Operation 712: the SMF sends an N4 session modification message to theUPF. The message includes PDU session information. The PDU sessioninformation includes a PDU session identifier, a QoS flow informationincluded in the PDU session, the EPS bearers needing data forwarding inthe EPS system in each PDU session, a mapping relationship between a QoSflow and an EPS bearer, and an EPS bearer identifier and/or QoSinformation of the EPS bearer. The message includes information receivedfrom the AMF for data forwarding. The message includes the informationof direct data forwarding or indirect data forwarding.

The N4 session modification message includes EPS bearer informationincluded in the PDU session. The EPS bearer information includes an EPSbearer identifier and tunnel information used by the EPS bearer for dataforwarding. The SMF informs the UPF the correspondence between a QoSflow and an EPS bearer in the PDU session. The UPF knows the QoS flowinformation of the PDU session in the 5G system. The UPF receives theEPS bearer information and the mapping relationship between a QoS flowand an EPS bearer in the PDU session, from the SMF.

The message also includes that source NG-RAN node supports dataforwarding of the PDU session tunnel and/or data forwarding of the E-RABtunnel.

For indirect data forwarding, the SMF allocates tunnel information fordata forwarding between the NG-RAN and the UPF, or the UPF allocatestunnel information for data forwarding between the NG-RAN and the UPFand sends it to the SMF. If the source NG-RAN supports data forwardingof the PDU session tunnel, the UPF allocates the data forwarding tunnelinformation for the PDU session corresponding to the EPS bearer acceptedfor data forwarding. If the source NG-RAN node supports data forwardingof the E-RAB tunnel, the UPF allocates the data forwarding tunnelinformation for the EPS bearer accepted for data forwarding. If thesource NG-RAN node supports data forwarding of the PDU session tunneland data forwarding of the E-RAB tunnel, the UPF determines to allocatethe data forwarding tunnel information for each PDU session or for eachE-RAB. The tunnel information includes a transport layer address and aTEID.

The UPF sends the allocated tunnel information for data forwarding tothe SMF. The SMF receives the N4 session modification response messagefrom the UPF. The message includes tunnel information allocated by theUPF for data forwarding between the NG-RAN and the UPF. For direct dataforwarding, the UPF does not need to allocate data forwarding tunnelinformation. According to the information received in operation 703 orin this operation, the UPF knows whether it is direct data forwarding orindirect data forwarding. For direct data forwarding, operation 712 mayalso not be performed.

Operation 713: the SMF sends an update SM context response message tothe AMF. For direct data forwarding, the message includes tunnelinformation for data forwarding, received by the SMF from the AMF. Thetunnel information is used for direct data forwarding, and is for eachEPS bearer. For indirect data forwarding, the message includes tunnelinformation allocated by the SMF or UPF for data forwarding between theNG-RAN and the UPF. The tunnel information may be for each PDU sessionor each E-RAB.

Operation 714: the AMF sends a handover command message to the NG-RAN.The message includes a target-to-source transparent container, tunnelinformation for data forwarding allocated by E-UTRAN or UPF or SMF. Thetunnel information for data forwarding is for each PDU session or eachE-RAB. For direct data forwarding, the tunnel information for dataforwarding is for each E-RAB for which data forwarding is accepted. Forindirect data forwarding, the tunnel information for data forwarding isfor each PDU session to which the QoS flow accepted for data forwardingbelongs. The message further includes established PDU sessioninformation and PDU session information that is not successfullyestablished. The established PDU session information includes theestablished QoS flow information and the QoS flow information that isnote successfully established.

Operation 715: the NG-RAN sends a handover command message to the UE.

The NG-RAN forwards the data.

If the NG-RAN receives the tunnel information for each PDU session, theNG-RAN forwards the data to the UPF. The NG-RAN forwards data of QoSflows accepted for data forwarding to the UPF on the tunnel for thecorresponding PDU session. The NG-RAN sends the data of each QoS flow tothe UPF on the user plane tunnel allocated for the PDU session. For thedownlink data, the NG-RAN sends downlink packets to the UPF on thetunnel allocated for downlink data forwarding. The UPF forwards the datato the SGW. The UPF adds the QFI corresponding to the QoS flow to thepacket header, and forwards the data received from the NG-RAN to the SGWthrough the user plane tunnel allocated for the mapped EPS bearer. TheUPF forwards the data of different QoS flows in the PDU session to theSGW through the user plane tunnel allocated for the mapped EPS beareraccording to the mapping relationship between a QoS flow and an EPSbearer. According to the mapping relationship between a QoS flow and anEPS bearer and the EPS bearer information accepted for data forwarding,the UPF knows the QoS flow accepted for data forwarding, and the UPFforwards the data of the QoS flow accepted for data forwarding to theSGW through the user plane tunnel allocated for the mapped EPS bearer.Corresponding to the QoS flow that not accepted for data forwarding,there is no corresponding data forwarding tunnel, and the UPF discardsthe data.

If the NG-RAN receives the tunnel information for each E-RAB, the NG-RANforwards the data of the QoS flow to the respective E-RAB tunnel. TheNG-RAN forwards the PDCP Service Data Unit (SDU) to the respective E-RABtunnel. The PDCP SDU does not have a sequence number (SN). For indirectdata forwarding, the data is sent to the UPF, and the UPF forwards thedata to the SGW. For direct data forwarding, the data is sent directlyto the target base station.

The SGW forwards the data to the E-UTRAN. The SGW sends the datareceived from the tunnel for each EPS bearer from the UPF to the E-UTRANthrough the corresponding tunnel allocated by the E-UTRAN. The SGWforwards the data to the E-UTRAN according to the session transmissionmode in the EPS.

The E-UTRAN receives the forwarded data from the E-RAB tunnel, and theE-UTRAN first sends the forwarded data to the UE, and then sends thedata received from the new S1-U to the UE.

During the establishment of the PDU session or the establishment of theGBR QoS flow, the UE receives the EPS QoS information and/or the EPSbearer identifier information mapped to the QoS flow from the network.The UE associates the ongoing QoS flow and the EPS bearer identifierincluded in the handover command message to establish a correspondencetherebetween. For the QoS flow without corresponding to EPS bearer, theUE may delete it.

Operation 716: the UE sends a handover complete message to the E-UTRAN.

Operation 717: the E-UTRAN sends a handover notify message to the MME.The message includes tunnel information allocated by the E-UTRAN fordownlink data transmission.

Operation 718: the MME sends a modification bearer request message tothe SGW. The message includes tunnel information used by the S1interface for downlink data transmission.

Operation 719: the SGW sends a modification bearer request message tothe SMF. The SMF may further have the function of the PGW control plane.The SGW allocates tunnel information for downlink data transmissionbetween the SGW and the UPF, wherein the tunnel information correspondsto each EPS bearer or each PDU session.

Operation 720: the SMF request a UPF session modification. The SMF mayfurther have the function of the PGW control plane. The SMF sends thetunnel information for the downlink data transmission between the SGWand the UPF allocated by the SGW to the UPF, wherein the tunnelinformation corresponds to each EPS bearer or each PDU session. The UPFsends a session modification response to the SMF. The UPF allocatestunnel information for uplink data transmission between the SGW and theUPF, and the UPF sends the tunnel information for the uplink datatransmission to the SMF.

Operation 721: the SMF sends a modification bearer response message tothe SGW. The message includes tunnel information for uplink datatransmission between the SGW and the UPF, which the information isallocated by the UPF.

Operation 722: the SGW sends a modification bearer response message tothe MME.

As such, the description of the third handover method of the applicationis completed, and the problem of data forwarding during the UE movingbetween the EPS and the 5GS system is completely solved by the methodwhen equipment from different vendors support different methods for dataforwarding, thereby avoiding data loss, ensuring service continuity andinteroperability of different equipment from different vendors, andreducing configuration by operator.

The fourth method for supporting handover according to the applicationis shown in FIG. 8.

FIG. 8 is a schematic diagram of a fourth method for supporting handoveraccording to an embodiment of the disclosure.

Referring to FIG. 8, the method is applicable to the second manner inwhich two data forwarding methods coexist, that is, which dataforwarding method is specifically supported depends on theimplementation of the NG-RAN node and the UPF. This method is used forthe handover from EPS to 5GS Detailed descriptions of operationsunrelated to the embodiment are omitted herein. This method includes theoperations of:

Operation 800: the E-UTRAN determines to hand over a UE to an NG-RAN.

Here, the E-UTRAN may be an eNB connected to the EPC. The NG-RAN may bea gNB, or a central unit (CU) in the eNB or gNB connected to the 5GC.The eNB connected to the 5GC may also be referred to as an ng-eNB.

The user plane path before handover is PGW-U+UPF (the UPF having thefunction of the PGW user plane, hereinafter referred to as UPF), the SGWto the E-UTRAN. The SGW needs to support the interface to connect withPGW-U+UPF. The UE has one or more PDU sessions in progress. Each PDUsession includes one or more EPS bearers. In a PDU session establishmentprocess or an EPS bearer establishment process, the mapped QoSinformation and/or the QoS flow identifier of the QoS flow are allocatedfor the EPS bearer. The default EPS bearer is mapped to a non-guaranteedbusiness rate (non-GBR) QoS flow. The QoS information and/or the QoSflow identifier of the QoS flow mapped to the EPS bearer may beallocated by the function of the PCC or the PGW control plane. In orderto support handover between different systems, the function of the PGWcontrol plane may further have an SMF function. In the scene ofdeploying the PCC, the policy control and charging rules function (PCRF)provides the QoS information and/or QoS flow identifier of the QoS flowmapped to the EPS bearer to the SMF. In order to support handoverbetween different systems, the PCRF may also have a policy controlfunction (PCF). The SMF sends the QoS information and/or QoS identifierof the QoS flow mapped to the EPS bearer to the UE through the MME, forexample, sending them to the UE through a non-access layer message PDNconnection establishment message. During the PDU session establishmentprocess or the EPS bearer establishment process, the SMF may also sendthe QoS information and/or QoS flow identifier of the QoS flow mapped tothe EPS bearer to the E-UTRAN through the MME. The E-UTRAN may send themapping information to the UE through an RRC message. The E-RAB and EPSbearer identifiers are the same or one-to-one correspondence, which arereferred to as an EPS bearer in the core network, and are referred to asan E-RAB in the access network. The E-RAB identifier and the EPS beareridentifier are the same or one-to-one correspondence, which are referredto as an EPS bearer identifier in the core network, and are referred toas an E-RAB identifier in the access network.

Operation 801: the E-UTRAN sends a handover required message to the MME.The message includes the identifier of the target NG-RAN node, and asource-to-target transparent container. The message also includesidentifier information indicating the AMF to which the target NG-RANnode is connected. The identifier information may be a tracking areaidentifier, a network sharding identifier, an AMF pool identifier, anAMF identifier or the like.

The message includes information of direct data forwarding pathavailability.

The source-to-target transparent container includes a PDU sessionidentifier, an identifier of the QoS flow in the PDU session, and thedownlink data forwarding proposed for the QoS flow. The eNB obtains thePDU session identifier corresponding to the EPS bearer and/or the QoSflow identifier in the PDU session through the PDN connectionestablishment process or through the handover process. It is alsopossible to obtain the QoS information of the mapped QoS flow. The eNBdetermines whether to propose data forwarding according to the E-RAB toPDU session or according to the mapping of the QoS flow in the E-RAB tothe PDU session and the QoS information, and the eNB may consider otherfactors such as whether there is buffered data to determine whether topropose data forwarding, without affecting the main content of theapplication.

Operation 802: the MME sends a forward relocation request message to theAMF. The MME selects and finds the AMF according to the identifierinformation of the AMF to which the target NG-RAN node is connected,which the information is included in the handover required message. Themessage includes the identifier of the target NG-RAN node, thesource-to-target transparent container and the UE context information.The UE context information includes UE mobile management (MM) contextinformation and a session management context. The message includes thehandover type.

The MME sends a direct forwarding indication to the AMF. If the MMEdoesn't receives direct data forwarding path availability from thesource E-UTRAN, the MME determines whether indirect data forwarding ispossible. The MME informs the AMF of the information of whether directdata forwarding or indirect data forwarding. The MME may also inform AMFof the information of data forwarding being not possible. Dataforwarding being not possible means that both direct data forwarding andindirect data forwarding are not possible.

Operation 803 a: the AMF sends a creation session (SM) context requestmessage to the SMF. The AMF converts the received EPS UE context into a5GS UE context. The AMF may also exchange with the PCRF to obtain theconverted 5GS UE context. The AMF selects the SMF that serves the UE.

According to the information received in the forward relocation requestmessage, the AMF knows that the handover is a handover between differentsystems, and the AMF requests the SMF to provide the SM context. The AMFsends the message to each SMF serving the UE.

The AMF sends the direct forwarding indication to the SMF, and the AMFinforms the SMF the information of whether direct data forwarding orindirect data forwarding is available.

The AMF informs the SMF of the information of whether direct dataforwarding or indirect data forwarding or data forwarding is notpossible.

Operation 804: the SMF initiates an N4 session modification processbetween it and the UPF. The SMF informs the UPF of the information ofwhether direct data forwarding or indirect data forwarding. The SMF mayalso inform UPF that data forwarding is not possible. The UPF informsthe SMF of the information of supporting the PDU session tunnel and/orE-RAB tunnel data forwarding. If direct data forwarding is possible andthe UPF supports E-RAB tunnel data forwarding, the UPF may inform theSMF of the information of supporting the E-RAB tunnel data forwarding.If data forwarding is not possible, UPF may not need to inform the SMFwhich manner of data forwarding is supported. If indirect dataforwarding is possible, the UPF informs the SMF of the information ofdata forwarding manner supported by the UPF actually, such as the PDUsession tunnel and/or E-RAB tunnel data forwarding.

Operation 803 b: the SMF sends a creation session context responsemessage to the AMF. The message includes the SM context of the UE. TheSM context also includes a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer contexttogether with the SM context to the AMF at the same time when the AMFrequests the SM context. Alternatively, the SMF sends the mapped EPSbearer context to the AMF only when the AMF requests the mapped EPScontext at the same time.

The 5GS UE context includes QoS information in the 5G system. The QoSinformation in the 5G system includes a QoS rule and/or a QoS profile.The AMF may map EPS QoS information into 5G QoS information, or the AMFinteracts with the 5G policy control function (5G-PCF) to derive 5G QoSinformation.

The SMF determines direct data forwarding, indirect data forwarding, ordata forwarding not possible. If the direct forwarding indicationreceived by the SMF indicates that direct data forwarding path isavailable, the SMF determines to use direct data forwarding. If thedirect forwarding indication received by the SMF indicates indirect dataforwarding and that indirect data forwarding is possible, the SMFdetermines to use indirect data forwarding. If the direct forwardingindication received by the SMF indicates indirect data forwarding but noindirect data forwarding connectivity between source and target, the SMFdetermines that data forwarding is not possible. The SMF includesinformation of direct data forwarding, indirect data forwarding, or dataforwarding being not possible in the N2 session management (SM)information container.

The message includes a data forwarding manner supported by the UPF, thatis, the information that the UPF supports PDU session tunnel and/orE-RAB tunnel data forwarding.

Operation 805: the AMF sends the handover request message to the NG-RAN.The message includes information of the PDU session to be established.The information of the PDU session includes a session identifier,session QoS information, QoS flow information, uplink tunnel informationfor each session, and/or a source-to-target transparent container. Themessage includes the type of handover.

The message includes the information of direct data forwarding, indirectdata forwarding, or data forwarding being not possible. The aboveinformation may be included in a N2 SM information container.

The message includes a data forwarding manner supported by the UPF, thatis, information that the UPF supports PDU session tunnel and/or E-RABtunnel data forwarding.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the E-RAB identifiermapped by the QoS flow and/or the mapped QoS information.

Operation 806: the NG-RAN sends a handover request acknowledgementmessage to the AMF. The message includes one or more of the followinginformation:

1) the target-to-source transparent container. The target-to-sourcetransparent container may further include a mapping relationship betweena QoS flow and an EPS bearer in the PDU session, that is, the EPS beareridentifier mapped by the QoS flow and/or the mapped QoS information.

2) the established PDU session information list accepted by the NG-RAN.The PDU session information list includes a PDU session identifier,downlink tunnel information of the NG3 interface used for the PDUsession, QoS flow information accepted by the PDU session, andunaccepted QoS flow information.

If the NG-RAN and the UPF support the E-RAB tunnel data forwarding, fora QoS flow accepted for data forwarding or a E-RAB accepted for dataforwarding by the NG-RAN, the NG-RAN allocates the downlink dataforwarding tunnel information to the respective E-RAB, and the E-RABidentifier and the downlink tunnel information for the E-RAB allocatedby the NG-RAN are included in the handover request acknowledgementmessage. If the NG-RAN and the UPF support the PDU session tunnel dataforwarding, for the QoS flow accepted for data forwarding by the NG-RAN,the NG-RAN allocates the downlink data forwarding tunnel information forthe PDU session to which the QoS flow belongs; the PDU sessionidentifier and the downlink tunnel information corresponding to PDUsession allocated by the NG-RAN are included in the handover requestacknowledgement message, and the QoS flow list accepted for dataforwarding may be further included in the handover requestacknowledgement message. If both the NG-RAN and the UPF support two dataforwarding manners (PDU session tunnel data forwarding manner and E-RABdata forwarding), the NG-RAN may determine to allocate which manner ofdata forwarding tunnel, and then the corresponding data forwardingtunnel information is included in the handover request acknowledgementmessage by the NG-RAN. If data forwarding is not possible, the NG-RANdoes not need to allocate data forwarding tunnel information. For directdata forwarding, only E-RAB tunnel for data forwarding may be used,which is available when both the NG-RAN and the UPF support the E-RABtunnel data forwarding.

3) the PDU session information list failed to be setup by the NG-RAN.The PDU session information list includes the PDU session identifier andthe reason for not accepting.

Operation 807: the AMF sends an update SM context request message to theSMF. If tunnel information for data forwarding is received from theNG-RAN, the AMF sends the data forwarding tunnel information receivedfrom the NG-RAN to the SMF. The AMF sends the tunnel informationreceived from the NG-RAN for data forwarding to the SMF. The AMF sendsthe information of whether it is direct data forwarding or indirect dataforwarding to the SMF. AMF may inform SMF of direct data forwarding orindirect data forwarding in an explicit manner. The AMF may also informthe SMF in an implicit manner, that is, if the SMF receives the dataforwarding tunnel information for each E-RAB, it is direct dataforwarding, and if the SMF receives the data forwarding tunnelinformation for each PDU session, it is indirect data forwarding, and ifno data forwarding tunnel information is received, data forwarding isnot feasible or data forwarding is not accepted by the target basestation. The message includes a PDU session to which the EPS bearerbelongs. The message may also include a mapping relationship between anEPS bearer and a QoS flow in the PDU session.

Operation 808: the SMF initiates a session modification process betweenit and the UPF. The SMF sends the information of whether direct dataforwarding or indirect data forwarding to the UPF. the SMF sends the NG3interface downlink data forwarding tunnel information allocated by theNG-RAN to the UPF through the N4 session modification process, whereinthe data forwarding tunnel information corresponds to each PDU sessionor each EPS bearer. The SMF allocates the data forwarding tunnelinformation between the SGW and the UPF, or the UPF allocates the tunnelinformation for data forwarding between the SGW and the UPF and sendsthe tunnel information to the SMF, wherein the data forwarding tunnelinformation is for each E-RAB. The N4 session modification messageincludes a PDU session to which the EPS bearer belongs. The N4 sessionestablishment or N4 session modification message may further include amapping relationship between an EPS bearer and a QoS flow in the PDUsession. For direct data forwarding, the SMF or UPF does not need toallocate the data forwarding tunnel information. According to theinformation received in operation 803 or in this operation, the UPFknows whether it is direct data forwarding or indirect data forwarding.Corresponding to the implicit manner, if the SMF receives the dataforwarding tunnel information for each E-RAB, it is direct dataforwarding.

Operation 809: the SMF sends an update SM context response message tothe AMF. The SMF sends the tunnel information for data forwarding to theAMF. Corresponding to direct data forwarding, the SMF sends the tunnelinformation for each E-RAB received from the AMF to the AMF, and thetunnel information for each E-RAB is allocated by the target NG-RAN.Corresponding to indirect data forwarding, the SMF sends the tunnelinformation for each E-RAB allocated by the SMF or UPF to the AMF, andthe tunnel information is used for data forwarding between the SGW andthe UPF.

Operation 810: the AMF sends a forward relocation response message tothe MME. The message includes data forwarding tunnel information. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN. For indirect data forwarding, the tunnel information istunnel information received from the SMF for data forwarding between theSGW and the UPF. The message includes a target-to-source transparentcontainer.

Operation 811: the MME sends a creating indirect data forwarding tunnelrequest message to the SGW for indirect data forwarding, if the MMEreceives the tunnel information for data forwarding. The message is usedto send tunnel information for data forwarding between the SGW and theUPF to the SGW. The SGW sends a creating indirect data forwarding tunnelresponse message to the MME. The message includes uplink tunnelinformation allocated by the SGW for data forwarding of the S1interface. For direct data forwarding, this operation is not required tobe performed.

Operation 812: the MME sends a handover command message to the E-UTRAN.The message includes a target-to-source transparent container. Themessage includes the type of handover.

The message includes data forwarding tunnel information. For indirectdata forwarding, the tunnel information is allocated by the SGW. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN.

Operation 813: the E-UTRAN sends a handover command message to the UE.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the EPS bearer identifierand/or the mapped QoS information mapped by the QoS flow.

The E-UTRAN forwards data. For the E-RAB for which the data forwardingtunnel information is received, it indicates that the target basestation accepts data forwarding, and the E-UTRAN forwards the data tothe corresponding tunnel. For direct data forwarding, the target NG-RANdirectly receives the data forwarded by the E-UTRAN. For indirect dataforwarding, the SGW receives the data forwarded by the E-UTRAN. The SGWforwards the data to the UPF. The SGW forwards data to the UPF for eachEPS bearer accepted for data forwarding on the corresponding tunnel. TheUPF forwards the data to the NG-RAN. According to the data forwardingtunnel information which is allocated by the NG-RAN and received inoperation 808, the UPF forwards the data to the NG-RAN through thecorresponding tunnel. If the received tunnel is for each PDU session,the UPF sends the data, belonging to the same PDU session, received fromthe SGW on the tunnel for each EPS bearer to the NG-RAN through the PDUsession tunnel, that is, the UPF performs mapping of multiple tunnels toone tunnel. The UPF forwards data to the NG-RAN according to the sessiontransmission manner in the 5GS, for example, through which several QoSflows to send downlink data in each PDU session, and how to set theheader of the QoS flow. The UPF adds a QoS flow identifier (QFI) to thepacket header forwarded to the target NG-RAN. If the received tunnel isfor each E-RAB, the UPF directly forwards the data to the correspondingE-RAB tunnel.

The NG-RAN receives the forwarded data from a PDU session tunnel, andthe NG-RAN sends the received data to the UE according to an existingmanner. The NG-RAN receives the forwarded data from an E-RAB tunnel, andthe NG-RAN directly sends the data to the PDCP layer of thecorresponding DRB with no need for SDAP layer processing. Based on themapping relationship between an E-RAB ID(s) and a QoS Flow ID(s)received in the handover request message, the NG-RAN knows the DRBcorresponding to the E-RAB, and directly sends the received forwardeddata to the PDCP entity of the corresponding DRB. The NG-RAN first sendsthe forwarded data to the UE, and then sends the data received from anew NG-U to the UE.

During the establishment of the PDU session or the establishment of theEPS bearer, the UE receives the QoS information of the QoS flow mappedby the EPS bearer and/or the QoS flow information from the network. TheUE establishes the correspondence between the ongoing EPS bearer and theQoS flow included in the handover command message. For an EPS bearerthat does not have a corresponding QoS flow, the UE may delete it.

Alternatively, the UE obtains the mapping relationship between a QoSflow and an EPS bearer in the PDU session from the handover commandmessage. The UE establishes the correspondence between the ongoing EPSbearer and the QoS flow included in the handover command message. For anEPS bearer that does not have a corresponding QoS flow, the UE maydelete it.

Operation 814: the UE sends, a handover complete message to the NG-RAN.

Operation 815: the NG-RAN sends a handover notify message to the AMF.The message includes the tunnel information allocated by the NG-RAN fordownlink data transmission.

Operation 816: the AMF sends an update SM context request message to theSMF.

Operation 817: the SMF sends a N4 session modification message to theUPF. The UPF sends the N4 session modification response message to theSMF.

The AMF sends the tunnel information allocated by the NG-RAN fordownlink data transmission to the UPF through the AMF.

Operation 818: the SMF sends an update SMF context response message tothe AMF.

As such, the description of the fourth handover method of theapplication is completed, and the problem of data forwarding during theUE moving between the EPS and the 5GS system is completely solved by themethod, when equipment from different vendors supports different methodsfor data forwarding, thereby avoiding data loss, ensuring servicecontinuity and interoperability of different equipment from differentvendors, and reducing configuration by operator.

The fifth method for supporting handover in the application is as shownin FIG. 9.

FIG. 9 is a schematic diagram of a fifth method for supporting handoveraccording to an embodiment of the disclosure.

Referring to FIG. 9, this method is applicable to the third manner inwhich two data forwarding methods coexist, that is, both data forwardingmethods are required to be supported. This method is used for handoverfrom 5GS to EPS. Detailed descriptions of operations unrelated to theembodiment are omitted herein. The method includes the operations of:

Operation 901: the NG-RAN determines to hand over the UE to the E-UTRAN.

The E-UTRAN herein may be an eNB connected to the EPC. The NG-RAN may bea gNB or a centralized unit CU in a gNB or an eNB connected to the SGC.

The user plane path before handover is UPF to NG-RAN. The SGW needs tosupport an interface to connect with the UPF. The UPF may include thefunction of the PGW user plane to perform the function of the user planeanchor node during the handover between different RATs.

The UE has one or more PDU sessions in progress. Each PDU sessionincludes one or more QoS flows. In a PDU session establishment processor a guaranteed business rate (GBR) QoS flow establishment process, themapped EPS QoS information and/or the EPS bearer identifier areallocated for the QoS flow. The non-guaranteed business rate (non-GBR)QoS flow is mapped to a default EPS bearer. The GBR QoS flow is mappedto an EPS dedicated bearer. The EPS QoS information mapped to the QoSflow may be allocated by the PCC or SMF. The EPS bearer identifiermapped to the QoS flow may be allocated by the SMF or AMF. Forsupporting the handover between different systems, the SMF may have thefunction of the PGW control plane. In the scene of deploying the PCC,the policy control function (PCF) provides the EPS QoS mapped to QoSflow to the SMF. In order to support handover between different systems,the PCF may also have a policy control and charging rules function(PCRF). The SMF sends the EPS QoS information and/or EPS beareridentifier mapped to the QoS flow to the UE through the AMF, forexample, sending them through a non-access layer message PDU sessionestablishment message to the UE. During the PDU session establishment orguaranteed business rate (GBR) QoS flow establishment process, the SMFmay also send the EPS QoS information and/or E-RAB identifier mapped tothe QoS flow to the NG-RAN through the AMF. The AMF sends the EPS QoSinformation and/or E-RAB identifier mapped to the QoS flow to the NG-RANthrough an initial context establishment request message or a PDUsession resource establishment request message. The NG-RAN may send theEPS QoS information or E-RAB identifier mapped to the QoS flow to the UEthrough an RRC message. The E-RAB and EPS bearer are the same orone-to-one correspondence, which are referred to as an EPS bearer in thecore network, and are referred to as an E-RAB in the access network. TheE-RAB identifier and the EPS bearer identifier are the same orone-to-one correspondence, which are referred to as an EPS beareridentifier in the core network, and are referred to as an E-RABidentifier in the access network.

Operation 902: the NG-RAN sends the handover required message to theAMF. The message includes the identifier of the target eNB, asource-to-target transparent container. The source-to-target transparentcontainer includes an E-RAB identifier and downlink data forwardingproposed for the E-RAB. The NG-RAN obtains the EPS bearer identifiermapped to the QoS flow in the PDU session through the PDU sessionestablishment process or through the handover process, as well mayobtain the mapped EPS QoS information. The NG-RAN determines whether topropose data forwarding according to the mapping of QoS flow to E-RABand the QoS information, and the NG-RAN may consider other factors suchas whether there is buffered data to determine whether to propose dataforwarding, without affecting the main concept of the application. Themessage includes information of direct forwarding path availability.

The message further includes identifier information indicating the MMEto which the target eNB is connected. The identifier information may bea tracking area identifier or an MME identifier.

The message also includes the handover type.

Operation 903 a: the AMF sends a session management (SM) context requestmessage to the SMF. Based on the information received in the handoverrequired message, the AMF knows that the handover is a handover betweendifferent systems, and the AMF requests the SMF to provide the SMcontext. The AMF may also request an EPS bearer context. The AMF sendsthe message to each SMF serving the UE. The message includes informationof direct data forwarding path availability. The SMF saves informationof whether direct data forwarding is feasible.

Operation 903 b: the SMF sends an N4 session modification requestmessage to the UPF. The message includes information of direct dataforwarding path availability. The UPF saves information of whetherdirect data forwarding is possible. The UPF sends an N4 sessionmodification response message to the SMF.

Operation 903 c: the SMF sends an SM context response message to theAMF. The message includes the SM context of the UE. The SM context alsoincludes the mapped EPS bearer context, such as EPS bearer identifierand/or the EPS QoS information. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer context alongwith the SM context to the AMF at the same time, when the AMF requeststhe SM context. Alternatively, the SMF sends the mapped EPS bearercontext to the AMF along with the SM context, only when the AMF requeststhe SM context and also requests the mapped EPS bearer context to theSMF.

Operation 904: the AMF sends a forward relocation request message to theMME. The AMF selects and finds the MME according to the identifierinformation of the MME connected to the target eNB included in thehandover required message. The identifier information of the MMEconnected to the target eNB may be a TAI. The message includes anidentifier of the target eNB, a source-to-target transparent container,and the mapped EPS UE context information. The mapped EPS UE contextinformation includes UE mobile management (MM) context information andsession SM context information.

If the AMF does not receive information of direct data forwarding pathavailability from the source NG-RAN, the AMF determines whether indirectdata forwarding is feasible. If direct data forwarding is feasible,direct data forwarding is used. The AMF informs the MME whether directdata forwarding or indirect data forwarding. The AMF may also inform theMME of the information of data forwarding being not feasible.

Operation 905: the MME sends a creation session request message to theSGW. The message includes EPS bearer context information.

Operation 906: the SGW sends a creation session response message to theMME. The message includes tunnel information for an S1 interface to senduplink data allocated by the SGW.

Operation 907: the MME sends a handover request message to the E-UTRAN.The message includes a source-to-target transparent container and E-EABcontext. The E-RAB context includes the E-RAB to be established anduplink tunnel information of the S1 interface allocated by the SGW. TheE-RAB context includes information of whether data forwarding ispossible. The message includes the handover type, and the specificcontent thereof is the same as that in Operation 902, which details arenot described herein again.

Operation 908: the E-UTRAN sends a handover request acknowledgementmessage to the MME. The message includes the established E-RAB list andthe E-RAB list failed to be established, as well as the target-to-sourcetransparent container. Corresponding to the established E-RAB, thetunnel information for downlink data transmission of the S1 interface isfurther included. Corresponding to the established E-RAB, if the sourcebase station proposes the downlink data forwarding, data forwarding ispossible, and the target eNB accepts the downlink data forwarding, thetarget base station includes the tunnel information for data forwardingallocated by the E-UTRAN for each E-RAB accepted for downlink dataforwarding.

Operation 909: the MME requests the SGW to create an indirect dataforwarding tunnel. This operation is performed only when indirect dataforwarding is applied. If the MME receives the downlink tunnelinformation for data forwarding from the E-UTRAN, the MME requests theSGW to create an indirect data forwarding tunnel. The MME sends thetransport layer address and TEID allocated by the eNB for dataforwarding to the SGW. The transport layer address and TEID correspondto each E-RAB.

The SGW sends an indirect data forwarding tunnel creation responsemessage to the MME. The message includes the information allocated bythe SGW for data forwarding between the SGW and the UPF. The informationused for data forwarding between the SGW and the UPF includes an E-RABidentifier and tunnel information used by the E-RAB for data forwarding.The tunnel information includes a transport layer address and a TEIDallocated by the SGW. The SGW allocates downlink data forwarding tunnelinformation for the E-RAB accepted for downlink data forwarding. The SGWallocates uplink data forwarding tunnel information for the E-RABaccepted for uplink data forwarding. The data forwarding tunnelinformation included in the E-RAB information may include uplink and/ordownlink data forwarding tunnel information.

Operation 909 is performed when indirect data forwarding is feasible.

Operation 910: the MME sends a forward relocation response message tothe AMF. The message includes tunnel information for data forwarding.For direct data forwarding, the data forwarding tunnel information isreceived from the target base station by the MME. For indirect dataforwarding, the tunnel information is allocated by the SGW and isreceived by the MME from the SGW. The tunnel information corresponds toeach EPS bearer. The tunnel information of data forwarding may includedownlink and/or uplink data forwarding tunnel information. The messageincludes a target-to-source transparent container.

The MME directly sends the E-RAB information to the AMF, and the AMFperforms the conversion.

Operation 911: the AMF sends an update SM context request message to theSMF. The message includes the information of direct data forwarding orindirect data forwarding. The AMF requests the SMF to create a dataforwarding tunnel. For indirect data forwarding, the AMF requests theSMF to create a data forwarding tunnel. The message includes PDU sessioninformation. The PDU session information includes a PDU sessionidentifier, a QoS flow information included in the PDU session, the EPSbearers needing data forwarding in the EPS system in each PDU session, amapping relationship between a QoS flow and an EPS bearer, an EPS beareridentifier and/or QoS information of the EPS bearer. The messageincludes tunnel information received from the MME for data forwarding.

Operation 912: the SMF sends an N4 session modification message to theUPF. The message includes PDU session information. The PDU sessioninformation includes a PDU session identifier, a QoS flow informationincluded in the PDU session, the EPS bearers needing data forwarding inthe EPS system in each PDU session, a mapping relationship between a QoSflow and an EPS bearer, and an EPS bearer identifier and/or QoSinformation of the EPS bearer. The message includes tunnel informationreceived from the AMF for data forwarding. The message includes theinformation of direct data forwarding or indirect data forwarding.

The N4 session modification message includes EPS bearer informationincluded in the PDU session. The EPS bearer information includes an EPSbearer identifier and tunnel information used by the EPS bearer for dataforwarding. The SMF informs the UPF the correspondence between a QoSflow and an EPS bearer in the PDU session. The UPF knows the QoS flowinformation of the PDU session in the 5G system. The UPF receives theEPS bearer information and the mapping relationship between a QoS flowand an EPS bearer in the PDU session, from the SMF.

The UPF determines whether the data forwarding tunnel between the NG-RANnode and the UPF is a PDU session tunnel or an E-RAB tunnel. The UPFallocates the tunnel information for data forwarding between the NG-RANand the UPF and sends the tunnel information to the SMF. If it isdetermined to use the PDU session tunnel for data forwarding, the UPFallocates the data forwarding tunnel information for the PDU sessioncorresponding to the EPS bearer accepted for data forwarding. If it isdetermined to use the E-RAB tunnel for data forwarding, the UPFallocates data forwarding tunnel information for the EPS bearer acceptedfor data forwarding. The tunnel information includes a transport layeraddress and a TEID.

The UPF sends the allocated tunnel information for data forwarding tothe SMF. The SMF receives the N4 session modification response messagefrom the UPF. The message includes tunnel information allocated by theUPF for data forwarding between the NG-RAN and the UPF. For direct dataforwarding, the UPF does not need to allocate data forwarding tunnelinformation. According to the information received in operation 903 orin this operation, the UPF knows whether it is direct data forwarding orindirect data forwarding. For direct data forwarding, operation 912 mayalso not be performed.

Operation 913: the SMF sends an update SM context response message tothe AMF. For direct data forwarding, the message includes tunnelinformation for data forwarding, received by the SMF from the AMF. Thetunnel information is used for direct data forwarding, and is for eachEPS bearer. For indirect data forwarding, the message includes tunnelinformation allocated by the UPF for data forwarding between the NG-RANand the UPF. The tunnel information may be for each PDU session or eachE-RAB.

Operation 914: the AMF sends a handover command message to the NG-RAN.The message includes a target-to-source transparent container, andtunnel information for data forwarding allocated by E-UTRAN or the UPFor SMF. The tunnel information for data forwarding is for each PDUsession or each E-RAB. For direct data forwarding, the tunnelinformation for data forwarding is for each E-RAB for which dataforwarding is accepted. For indirect data forwarding, the tunnelinformation for data forwarding is for each PDU session to which the QoSflow accepted for data forwarding belongs. The message further includesestablished PDU session information and PDU session information that isnot successfully established. The established PDU session informationincludes the established QoS flow information and the QoS flowinformation that is note successfully established.

Operation 915: the NG-RAN sends a handover command message to the UE.

The NG-RAN forwards the data.

If the NG-RAN receives the data forwarding tunnel information for eachPDU session, the NG-RAN forwards the data to the UPF. The NG-RANforwards data of QoS flows accepted for data forwarding to the UPF onthe tunnel the corresponding PDU session. For the downlink data, theNG-RAN sends downlink packets to the UPF on the tunnel allocated fordownlink data forwarding. The UPF forwards the data to the SGW. The UPFadds the QFI corresponding to the QoS flow to the packet header, andforwards the data received from the NG-RAN to the SGW through the userplane tunnel allocated for the mapped EPS bearer. The UPF forwards thedata of different QoS flows in the PDU session to the SGW through theuser plane tunnel allocated for the mapped EPS bearer according to themapping relationship between the QoS flow and the EPS bearer. Accordingto the mapping relationship between the QoS flow and the EPS bearer andthe EPS bearer information accepted for data forwarding, the UPF knowsthe QoS flow accepted for data forwarding, and the UPF forwards the dataof the QoS flow accepted for data forwarding to the SGW through the userplane tunnel allocated for the mapped EPS bearer. Corresponding to theQoS flow that not accepted for data forwarding, there is nocorresponding data forwarding tunnel, and the UPF discards the data.

If the NG-RAN receives the data forwarding tunnel information for eachE-RAB, the NG-RAN forwards the data of the QoS flow to the respectiveE-RAB tunnel. The NG-RAN forwards the PDCP SDU to the respective E-RABtunnel. The PDCP SDU does not have an SN. For indirect data forwarding,the data is sent to the UPF, and the UPF forwards the data to the SGW.For direct data forwarding, the data is sent directly to the target basestation.

The SGW forwards the data to the E-UTRAN. The SGW sends the datareceived from the tunnel for each EPS bearer from the UPF to the E-UTRANthrough the corresponding tunnel allocated by the E-UTRAN. The SGWforwards the data to the E-UTRAN according to the session transmissionmode in the EPS.

The E-UTRAN receives the forwarded data from the E-RAB tunnel, and theE-UTRAN first sends the forwarded data to the UE, and then sends thedata received from the new S1-U to the UE.

During the establishment of the PDU session or the establishment of theGBR QoS flow, the UE receives the EPS QoS information and/or the EPSbearer identifier information mapped to the QoS flow from the network.The UE associates the ongoing QoS flow and the EPS bearer identifierincluded in the handover command message to establish a correspondencetherebetween. For the QoS flow without corresponding to EPS bearer, theUE may delete it.

Operation 916: the UE sends a handover complete message to the E-UTRAN.

Operation 917: the E-UTRAN sends a handover notify message to the MME.The message includes tunnel information allocated by the E-UTRAN fordownlink data transmission.

Operation 918: the MME sends a modification bearer request message tothe SGW. The message includes tunnel information used by the S1interface for downlink data transmission.

Operation 919: the SGW sends a modification bearer request message tothe SMF. The SMF may further have the function of the PGW control plane.The SGW allocates tunnel information for downlink data transmissionbetween the SGW and the UPF, wherein the tunnel information correspondsto each EPS bearer or each PDU session.

Operation 920: the SMF request a UPF session modification. The SMF mayfurther have the function of the PGW control plane. The SMF sends thetunnel information for the downlink data transmission between the SGWand the UPF allocated by the SGW to the UPF, wherein the tunnelinformation corresponds to each EPS bearer or each PDU session. The UPFsends a session modification response to the SMF. The UPF allocatestunnel information for uplink data transmission between the SGW and theUPF, and the UPF sends the tunnel information for the uplink datatransmission to the SMF.

Operation 921: the SMF sends a modification bearer response message tothe SGW. The message includes tunnel information for uplink datatransmission between the SGW and the UPF, which the information isallocated by the UPF.

Operation 922: the SGW sends a modification bearer response message tothe MME.

As such, the description of the fifth handover method of the applicationis completed, and the problem of data forwarding during the UE movingbetween the EPS and the 5GS system is completely solved by the method,when equipment from different vendors supports different methods fordata forwarding, thereby avoiding data loss, ensuring service continuityand interoperability of different equipment from different vendors, andreducing configuration by operator.

The sixth method for supporting handover in the application is shown asin FIG. 10.

FIG. 10 is a schematic diagram of a sixth method for supporting handoveraccording to an embodiment of the disclosure.

Referring to FIG. 10, this method is applicable to the third manner inwhich two data forwarding methods coexist, that is, both data forwardingmethods are required to be supported. This method is used for handoverfrom 5GS to EPS. Detailed descriptions of operations unrelated to theembodiment are omitted herein. The method includes the operations of:

Operation 1000: the E-UTRAN determines to hand over a UE to an NG-RAN.

Here, the E-UTRAN may be an eNB connected to the EPC. The NG-RAN may bea gNB, or a central unit (CU) in the eNB or gNB connected to the 5GC.The eNB connected to the 5GC may also be referred to as an ng-eNB.

The user plane path before handover is PGW-U+UPF (the UPF having thefunction of the PGW user plane, hereinafter referred to as UPF), the SGWto the E-UTRAN. The SGW needs to support the interface to connect withPGW-U+UPF. The UE has one or more PDU sessions in progress. Each PDUsession includes one or more EPS bearers. In a PDU session establishmentprocess or an EPS bearer establishment process, the mapped QoSinformation and/or the QoS flow identifier of the QoS flow are allocatedfor the EPS bearer. The default EPS bearer is mapped to a non-guaranteedbusiness rate (non-GBR) QoS flow. The QoS information and/or the QoSflow identifier of the QoS flow mapped to the EPS bearer may beallocated by the function of the PCC or the PGW control plane. In orderto support handover between different systems, the function of the PGWcontrol plane may further have an SMF function. In the scene ofdeploying the PCC, the policy control and charging rules function (PCRF)provides the QoS information and/or QoS flow identifier of the QoS flowmapped to the EPS bearer to the SMF. In order to support handoverbetween different systems, the PCRF may also have a policy controlfunction (PCF). The SMF sends the QoS information and/or QoS identifierof the QoS flow mapped to the EPS bearer to the UE through the MME, forexample, sending them to the UE through a non-access layer message PDNconnection establishment message. During the PDU session establishmentprocess or the EPS bearer establishment process, the SMF may also sendthe QoS information and/or QoS flow identifier of the QoS flow mapped tothe EPS bearer to the E-UTRAN through the MME. The E-UTRAN may send themapping information to the UE through an RRC message. The E-RAB and EPSbearer identifiers are the same or one-to-one correspondence, which arereferred to as an EPS bearer in the core network, and are referred to asan E-RAB in the access network. The E-RAB identifier and the EPS beareridentifier are the same or one-to-one correspondence, which are referredto as an EPS bearer identifier in the core network, and are referred toas an E-RAB identifier in the access network.

Operation 1001: the E-UTRAN sends a handover required message to theMME. The message includes the identifier of the target NG-RAN node, anda source-to-target transparent container. The message also includesidentifier information indicating the AMF to which the target NG-RANnode is connected. The identifier information may be a tracking areaidentifier, a network sharding identifier, an AMF pool identifier, anAMF identifier or the like.

The message includes information of direct data forwarding pathavailability.

The source-to-target transparent container includes a PDU sessionidentifier, an identifier of the QoS flow in the PDU session, and thedownlink data forwarding proposed for the QoS flow. The eNB obtains thePDU session identifier corresponding to the EPS bearer and/or the QoSflow identifier in the PDU session through the PDN connectionestablishment process or through the handover process. It is alsopossible to obtain the QoS information of the mapped QoS flow. The eNBdetermines whether to propose data forwarding according to the E-RAB toPDU session or according to the mapping of the QoS flow in the E-RAB tothe PDU session and the QoS information, and the eNB may consider otherfactors such as whether there is buffered data to determine whether topropose data forwarding, without affecting the main content of theapplication.

Operation 1002: the MME sends a forward relocation request message tothe AMF. The MME selects and finds the AMF according to the identifierinformation of the AMF to which the target NG-RAN node is connected. Themessage includes the identifier of the target NG-RAN node, thesource-to-target transparent container and the UE context information.The UE context information includes UE mobile management (MM) contextinformation and a session management context. The message includes thehandover type.

The MME sends a direct forwarding indication to the AMF. If the MMEdoesn't receives direct data forwarding path availability from thesource E-UTRAN, the MME determines whether indirect data forwarding ispossible. The MME informs the AMF of the information of whether directdata forwarding or indirect data forwarding. The MME may also inform AMFof the information of data forwarding being not possible. Dataforwarding being not possible means that both direct data forwarding andindirect data forwarding are not possible. Alternatively, the MME sendsthe information of direct data forwarding path availability to the AMF.

Operation 1003 a: the AMF sends a creation session (SM) context requestmessage to the SMF. The AMF converts the received EPS UE context into a5GS UE context. The AMF may also exchange with the PCRF to obtain theconverted 5GS UE context. The AMF selects the SMF that serves the UE.

According to the information received in the forward relocation requestmessage, the AMF knows that the handover is a handover between differentsystems, and the AMF requests the SMF to provide the SM context. The AMFsends the message to each SMF serving the UE.

The AMF sends the direct forwarding indication to the SMF, and the AMFinforms the SMF of the information that direct data forwarding orindirect data forwarding is available.

The AMF informs the SMF of the information of direct data forwarding orindirect data forwarding or data forwarding being not feasible. The AMFmay further inform the SMF of the information that direct dataforwarding is available.

Operation 1004: the SMF initiates an N4 session modification processbetween it and the UPF. The SMF informs the UPF of the information ofwhether direct data forwarding or indirect data forwarding. The SMF mayalso inform the UPF of the information that data forwarding is notpossible. The SMF may also inform the UPF of the information that directdata forwarding is available.

Operation 1003 b: the SMF sends a creation session context responsemessage to the AMF. The message includes the SM context of the UE. TheSM context also includes a mapping relationship between an EPS bearerand a QoS flow in the PDU session. If the SMF has the mapped EPS bearercontext, the SMF always feeds back the mapped EPS bearer contexttogether with the SM context to the AMF at the same time when the AMFrequests the SM context. Alternatively, the SMF sends the mapped EPSbearer context to the AMF when the AMF requests the mapped EPS contextat the same time.

The 5GS UE context includes QoS information in the 5G system. The QoSinformation in the 5G system includes a QoS rule and/or a QoS profile.The AMF may map EPS QoS information into 5G QoS information, or the AMFinteracts with the 5G policy control function (5G-PCF) to derive 5G QoSinformation.

The SMF determines direct data forwarding, indirect data forwarding, ordata forwarding not possible. If the direct forwarding indicationreceived by the SMF indicates that direct data forwarding is available,the SMF determines to use direct data forwarding. If the directforwarding indication received by the SMF indicates indirect dataforwarding and that indirect data forwarding is possible, the SMFdetermines to use indirect data forwarding. If the direct forwardingindication received by the SMF indicates indirect data forwarding but noindirect data forwarding connectivity, the SMF determines that dataforwarding is not possible. The SMF includes information of direct dataforwarding, indirect data forwarding, or data forwarding being notpossible in the N2 session management (SM) information container. Directdata forwarding information may be information of direct data forwardingpath availability. Data forwarding being not possible means thatindirect data forwarding is not possible or both direct and indirectdata forwarding are not possible.

The SMF determines that indirect data forwarding or data forwarding isnot feasible. The SMF informs the target NG-RAN of the information. Or,

the SMF determines whether indirect data forwarding is not possible. TheSMF informs the target NG-RAN of the information that indirect dataforwarding is not possible and whether direct data forwarding isavailable.

Operation 1005: the AMF sends the handover request message to theNG-RAN. The message includes information of the PDU session to beestablished. The information of the PDU session includes a sessionidentifier, session QoS information, QoS flow information, uplink tunnelinformation for each session, and/or a source-to-target transparentcontainer. The message includes the type of handover.

The message includes the information of direct data forwarding, indirectdata forwarding, or data forwarding being not possible. The aboveinformation may be included in a N2 SM information container. Directdata forwarding information may be information of direct data forwardingpath availability. Data forwarding being not possible means thatindirect data forwarding is not possible or both direct and indirectdata forwarding are not possible. The message may also include a mappingrelationship between a QoS flow and an EPS bearer in the PDU session,that is, the E-RAB identifier mapped by the QoS flow and/or the mappedQoS information.

Operation 1006: the NG-RAN sends a handover request acknowledgementmessage to the AMF. The message includes one or more of the followinginformation:

1) the target-to-source transparent container. The target-to-sourcetransparent container may further include a mapping relationship betweena QoS flow and an EPS bearer in the PDU session, that is, the EPS beareridentifier mapped by the QoS flow and/or the mapped QoS information.

2) the established PDU session information list accepted by the NG-RAN.The PDU session information list includes a PDU session identifier,downlink tunnel information of the NG3 interface used for the PDUsession, QoS flow information accepted by the PDU session, andunaccepted QoS flow information.

The NG-RAN determines whether the data forwarding tunnel is for each PDUsession or each E-RAB. If direct data forwarding is feasible, the NG-RANmay determine to use the E-RAB tunnel for data forwarding, and thehandover request acknowledgement message includes the E-RAB identifierand the downlink tunnel information for the E-RAB allocated by theNG-RAN. If it is indirect data forwarding, the NG-RAN determines whetherthe tunnel used for data forwarding between the NG-RAN and the UPF isfor each PDU session or each E-RAB. If it is determined to use the PDUsession tunnel for data forwarding, the NG-RAN allocates data forwardingtunnel information for the PDU session to which the QoS flow acceptedfor data forwarding belongs, and the handover request acknowledgementmessage includes the PDU session identifier and the downlink tunnelinformation corresponding to the PDU session allocated by the NG-RAN,and may further include a QoS flow list accepted for data forwarding. Ifit is determined to use the E-RAB tunnel for data forwarding, the NG-RANallocates data forwarding tunnel information for the E-RAB correspondingto the QoS flow or the E-RAB accepted for data forwarding, and thehandover request acknowledgement message includes the E-RAB identifierand the downlink tunnel information for the E-RAB allocated by theNG-RAN. The tunnel information includes a transport layer address and aTEID. The NG-RAN sends the allocated data forwarding tunnel informationto the AMF. If data forwarding is not possible, the NG-RAN does not needto allocate data forwarding tunnel information. For direct dataforwarding, only E-RAB tunnel for data forwarding may be used.

3) the PDU session information list failed to be setup by the NG-RAN.The PDU session information list includes the PDU session identifier andthe reason for not accepting.

Operation 1007: the AMF sends an update SM context request message tothe SMF. If tunnel information for data forwarding is received from theNG-RAN, the AMF sends the data forwarding tunnel information receivedfrom the NG-RAN to the SMF. The AMF sends the tunnel informationreceived from the NG-RAN for data forwarding to the SMF. The AMF sendsthe information of whether it is direct data forwarding or indirect dataforwarding to the SMF. The AMF may inform SMF of direct data forwarding,indirect data forwarding or data forwarding in an explicit manner. TheAMF may also inform the SMF of direct data forwarding or indirect dataforwarding in an implicit manner, that is, if the tunnel used for dataforwarding is a PDU session, it is indirect data forwarding, and if itis the tunnel information of the EPS bearer, it is direct dataforwarding. If no data forwarding tunnel information is received, dataforwarding is not feasible or data forwarding is not accepted by thetarget base station. The message includes a PDU session to which the EPSbearer belongs. The message may also include a mapping relationshipbetween an EPS bearer and a QoS flow in the PDU session.

Operation 1008: the SMF initiates a session modification process betweenit and the UPF. The SMF sends the information of whether direct dataforwarding or indirect data forwarding to the UPF. The SMF sends the NG3interface downlink data forwarding tunnel information allocated by theNG-RAN to the UPF through the N4 session modification process, whereinthe data forwarding tunnel information corresponds to each PDU sessionor each EPS bearer. The SMF allocates the data forwarding tunnelinformation between the SGW and the UPF, or the UPF allocates the tunnelinformation for data forwarding between the SGW and the UPF and sendsthe tunnel information to the SMF, wherein the data forwarding tunnelinformation is for each E-RAB. The N4 session modification messageincludes a PDU session to which the EPS bearer belongs. The N4 sessionestablishment or N4 session modification message may further include amapping relationship between an EPS bearer and a QoS flow in the PDUsession. For direct data forwarding, the SMF or UPF does not need toallocate the data forwarding tunnel information. According to theinformation received in operation 1003 or in this operation, the UPFknows whether it is direct data forwarding or indirect data forwarding.Corresponding to the implicit manner, if the SMF receives the dataforwarding tunnel information for each E-RAB, it is direct dataforwarding.

Operation 1009: the SMF sends an update SM context response message tothe AMF. The SMF sends the tunnel information for data forwarding to theAMF. Corresponding to direct data forwarding, the SMF sends the tunnelinformation for each E-RAB received from the AMF to the AMF, and thetunnel information for each E-RAB is allocated by the target NG-RAN.Corresponding to indirect data forwarding, the SMF sends the tunnelinformation for each E-RAB allocated by the SMF or UPF to the AMF, andthe tunnel information is used for data forwarding between the SGW andthe UPF.

Operation 1010: the AMF sends a forward relocation response message tothe MME. The message includes data forwarding tunnel information. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN. For indirect data forwarding, the tunnel information istunnel information received from the SMF for data forwarding between theSGW and the UPF. The message includes a target-to-source transparentcontainer.

Operation 1011: the MME sends a creating indirect data forwarding tunnelrequest message to the SGW for indirect data forwarding, if the MMEreceives the tunnel information for data forwarding. The message is usedto send tunnel information for data forwarding between the SGW and theUPF to the SGW. The SGW sends a creating indirect data forwarding tunnelresponse message to the MME. The message includes uplink tunnelinformation allocated by the SGW for data forwarding over the S1interface. For direct data forwarding, this operation is not required tobe performed. The MME knows whether it is direct data forwarding orindirect data forwarding according to the information of directforwarding path availability received from the source base station, asdescribed in operation 1002.

Operation 1012: the MME sends a handover command message to the E-UTRAN.The message includes a target-to-source transparent container. Themessage includes the type of handover.

The message includes data forwarding tunnel information. For indirectdata forwarding, the tunnel information is allocated by the SGW. Fordirect data forwarding, the tunnel information is allocated by thetarget NG-RAN.

Operation 1013: the E-UTRAN sends a handover command message to the UE.

The message may also include a mapping relationship between a QoS flowand an EPS bearer in the PDU session, that is, the EPS bearer identifierand/or the mapped QoS information mapped by the QoS flow.

The E-UTRAN forwards data. For the E-RAB for which the data forwardingtunnel information is received, it indicates that the target basestation accepts data forwarding, and the E-UTRAN forwards the data tothe corresponding tunnel. For direct data forwarding, the target NG-RANdirectly receives the data forwarded by the E-UTRAN. For indirect dataforwarding, the SGW receives the data forwarded by the E-UTRAN. The SGWforwards the data to the UPF. The SGW forwards data to the UPF for eachEPS bearer accepted for data forwarding on the corresponding tunnel. TheUPF forwards the data to the NG-RAN. The UPF forwards the data to theNG-RAN through the corresponding tunnel according to the data forwardingtunnel information allocated by the NG-RAN received in operation 1008.If the received tunnel is for each PDU session, the UPF sends the data,belonging to the same PDU session, received from the SGW on the tunnelfor each EPS bearer to the NG-RAN through the PDU session tunnel, thatis, the UPF performs mapping of multiple tunnels to one tunnel. The UPFforwards data to the NG-RAN according to the session transmission mannerin the 5GS, for example, through which several QoS flows to senddownlink data in each PDU session, and how to set the header of the QoSflow. The UPF adds a QoS flow identifier (QFI) to the packet headerforwarded to the target NG-RAN. If the received tunnel is for eachE-RAB, the UPF directly forwards the data to the corresponding E-RABtunnel.

The NG-RAN receives the forwarded data from a PDU session tunnel, andthe NG-RAN sends the received data to the UE according to an existingmanner. The NG-RAN receives the forwarded data from an E-RAB tunnel, andthe NG-RAN directly sends the data to the PDCP layer of thecorresponding DRB with no need for SDAP layer processing. Based on themapping relationship between an E-RAB ID(s) and a QoS Flow ID(s)received in the handover request message, the NG-RAN knows the DRBcorresponding to the E-RAB, and directly sends the received forwardeddata to the PDCP entity of the corresponding DRB. The NG-RAN first sendsthe forwarded data to the UE, and then sends the data received from anew NG-U to the UE.

During the establishment of the PDU session or the establishment of theEPS bearer, the UE receives the QoS information of the QoS flow mappedby the EPS bearer and/or the QoS flow information from the network. TheUE establishes the correspondence between the ongoing EPS bearer and theQoS flow included in the handover command message. For an EPS bearerthat does not have a corresponding QoS flow, the UE may delete it.

Alternatively, the UE obtains the mapping relationship between a QoSflow and an EPS bearer in the PDU session from the handover commandmessage. The UE establishes the correspondence between the ongoing EPSbearer and the QoS flow included in the handover command message. For anEPS bearer that does not have a corresponding QoS flow, the UE maydelete it.

Operation 1014: the UE sends a handover complete message to the NG-RAN.

Operation 1015: the NG-RAN sends a handover notify message to the AMF.The message includes the tunnel information allocated by the NG-RAN fordownlink data transmission.

Operation 1016: the AMF sends an update SM context request message tothe SMF.

Operation 1017: the SMF sends a N4 session modification message to theUPF. The UPF sends the N4 session modification response message to theSMF.

The AMF sends the tunnel information allocated by the NG-RAN fordownlink data transmission to the UPF through the AMF.

Operation 1018: the SMF sends an update SMF context response message tothe AMF.

As such, the description of the sixth handover method of the applicationis completed, and the problem of data forwarding during the UE movingbetween the EPS and the 5GS system is completely solved by the method,when equipment from different vendors support different methods for dataforwarding, thereby avoiding data loss, ensuring service continuity andinteroperability of different equipment from different vendors, andreducing configuration by operator.

Based on the same concept, an embodiment of the application provides anequipment, wherein the equipment may be any one of the foregoingequipment, for example, a source base station, a source core network, atarget core network, a target base station, a UPF, an SMF, an AMF, anNG-RAN node, and the equipment includes: a transceiver and a processor,

The transceiver is configured to send and receive signals;

The processor is configured to perform the method performed by any oneof the foregoing equipment.

Based on the same concept, an embodiment of the application provides acomputer readable storage medium having a computer program storedthereon, and implementing, when the program is executed by a processor,the method shown in the above described embodiments.

In particular, those skilled in the art will appreciate that theapplication includes equipment for performing one or more of theoperations described herein, including a full-duplex transceiver and anelectronic device. These may be specially designed and manufactured forrequired purposes, or may also include known devices in ageneral-purpose computer. This equipment has computer programs storedtherein that are selectively activated or reconfigured. Such computerprograms may be stored in a device (e.g., a computer) readable medium orin any type of medium suitable for storing electronic instructions andrespectively coupling to a bus, including but not limited to, any typesof disks (including floppy disks, hard disk, optical disks, CD-ROMs, andmagnetic-optical disks), read-only memory (ROM), random access memory(RAM), erasable programmable ROM (EPROM), electrically erasableprogrammable ROM (EEPROM), flash memory, magnetic or optical cards. Thatis, the readable medium includes any medium in which the information isstored or sent by a device (e.g., a computer) in a readable form.

The embodiment of the application provides a computer readable storagemedium suitable for the foregoing method embodiments, which will not berepeated herein.

It should be understood that although the various steps in the flowchartof the drawings are sequentially displayed as indicated by the arrows,these steps are not necessarily performed in the order indicated by thearrows. Except as explicitly stated herein, the execution of these stepsis not strictly limited, and may be performed in other sequences.Moreover, at least some of the steps in the flowchart of the drawingsmay include a plurality of sub-steps or stages, which are notnecessarily performed at the same time, but may be executed at differenttimes, and the order of execution thereof is not necessarily to beperformed sequentially, but may be performed alternately or alternatelywith at least a portion of the sub-steps or stages of other steps orother steps.

While the disclosure has been shown and described with reference tovarious embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the disclosure as definedby the appended claims and their equivalents.

What is claimed is:
 1. A method for supporting handover performed by atarget base station in a mobile communication system, the methodcomprising: receiving, from a target core network, a handover requestmessage including first information associated with a data forwarding;determining whether to accept the data forwarding based on the firstinformation; transmitting, to the target core network, a handoverrequest acknowledge message including tunnel information for the dataforwarding in case that the data forwarding is accepted; and receiving adownlink data forwarded from a source base station related to a sourcecore network according to the tunnel information.
 2. The method of claim1, wherein the target base station and the target core network areassociated with 5G system (5GS), and wherein the source base station andthe source core network are associated with evolved packet system (EPS).3. The method of claim 1, wherein second information on a directforwarding path availability for the data forwarding of the source basestation is transferred to the target core network.
 4. The method ofclaim 3, wherein the first information indicates that the dataforwarding is not possible or whether a direct forwarding path for thedata forwarding is available based on the second information.
 5. Themethod of claim 1, wherein in case that the first information indicatesa direct data forwarding, the tunnel information includes at least onebearer identifier between the source core network and the source basestation for the data forwarding.
 6. The method of claim 1, wherein incase that an indirect data forwarding is applied, the tunnel informationincludes at least one session identifier between the target core networkand the target base station for the data forwarding.
 7. A method forsupporting handover performed by a source base station in a mobilecommunication system, the method comprising: transmitting, to a sourcecore network, a handover required message including second informationon a direct forwarding path availability for a data forwarding;receiving, from the source core network, a handover command messageincluding bearer information for which a target base station related toa target core network has accepted the data forwarding; and forwarding adownlink data to the target base station based on the bearerinformation.
 8. The method of claim 7, wherein the target base stationand the target core network are associated with 5G system (5GS), andwherein the source base station and the source core network areassociated with evolved packet system (EPS).
 9. The method of claim 7,wherein the second information is transferred to the target corenetwork, and wherein first information associated with the dataforwarding is transmitted to the target base station, the firstinformation indicating that the data forwarding is not possible orwhether a direct forwarding path for the data forwarding is availablebased on the second information.
 10. The method of claim 9, whereinwhether the data forwarding is accepted by the target base station isbased on the first information.
 11. A target base station for supportinghandover in a mobile communication system, the target base stationcomprising: a transceiver; and a controller configured to: receive, froma target core network via the transceiver, a handover request messageincluding first information associated with a data forwarding, determinewhether to accept the data forwarding based on the first information,transmit, to the target core network via the transceiver, a handoverrequest acknowledge message including tunnel information for the dataforwarding in case that the data forwarding is accepted, and receive,via the transceiver, a downlink data forwarded from a source basestation related to a source core network according to the tunnelinformation.
 12. The target base station of claim 11, wherein the targetbase station and the target core network are associated with 5G system(5GS), and wherein the source base station and the source core networkare associated with evolved packet system (EPS).
 13. The target basestation of claim 11, wherein second information on a direct forwardingpath availability for the data forwarding of the source base station istransferred to the target core network.
 14. The target base station ofclaim 13, wherein the first information indicates that the dataforwarding is not possible or whether a direct forwarding path for thedata forwarding is available based on the second information.
 15. Thetarget base station of claim 11, wherein in case that the firstinformation indicates a direct data forwarding, the tunnel informationincludes at least one bearer identifier between the source core networkand the source base station for the data forwarding.
 16. The target basestation of claim 11, wherein in case that an indirect data forwarding isapplied, the tunnel information includes at least one session identifierbetween the target core network and the target base station for the dataforwarding.
 17. A source base station for supporting handover in amobile communication system, the source base station comprising: atransceiver; and a controller configured to: transmit, to a source corenetwork via the transceiver, a handover required message includingsecond information on a direct forwarding path availability for a dataforwarding, receive, from the source core network via the transceiver, ahandover command message including bearer information for which a targetbase station related to a target core network has accepted the dataforwarding, and forward a downlink data to the target base station basedon the bearer information.
 18. The source base station of claim 17,wherein the target base station and the target core network areassociated with 5G system (5GS), and wherein the source base station andthe source core network are associated with evolved packet system (EPS).19. The source base station of claim 17, wherein the second informationis transferred to the target core network, and wherein first informationassociated with the data forwarding is transmitted to the target basestation, the first information indicating that the data forwarding isnot possible or whether a direct forwarding path for the data forwardingis available based on the second information.
 20. The source basestation of claim 19, wherein whether the data forwarding is accepted bythe target base station is based on the first information.